diff --git a/filter/mathjaxloader/db/upgrade.php b/filter/mathjaxloader/db/upgrade.php
index c01643f2a54..9b64471bc64 100644
--- a/filter/mathjaxloader/db/upgrade.php
+++ b/filter/mathjaxloader/db/upgrade.php
@@ -31,129 +31,6 @@ defined('MOODLE_INTERNAL') || die();
 function xmldb_filter_mathjaxloader_upgrade($oldversion) {
     global $CFG;
 
-    require_once($CFG->dirroot . '/filter/mathjaxloader/db/upgradelib.php');
-
-    if ($oldversion < 2017040300) {
-
-        $httpsurl = get_config('filter_mathjaxloader', 'httpsurl');
-        $newcdnurl = filter_mathjaxloader_upgrade_cdn_cloudflare($httpsurl, false);
-
-        set_config('httpsurl', $newcdnurl, 'filter_mathjaxloader');
-
-        $mathjaxconfig = get_config('filter_mathjaxloader', 'mathjaxconfig');
-        if (strpos($mathjaxconfig, 'MathJax.Ajax.config.path') === false) {
-            $newconfig = 'MathJax.Ajax.config.path["Contrib"] = "{wwwroot}/filter/mathjaxloader/contrib";' . "\n";
-            $newconfig .= $mathjaxconfig;
-
-            set_config('mathjaxconfig', $newconfig, 'filter_mathjaxloader');
-        }
-
-        upgrade_plugin_savepoint(true, 2017040300, 'filter', 'mathjaxloader');
-    }
-
-    if ($oldversion < 2017042602) {
-
-        $httpsurl = get_config('filter_mathjaxloader', 'httpsurl');
-        if ($httpsurl === "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js") {
-            set_config('httpsurl', 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js', 'filter_mathjaxloader');
-        }
-
-        $mathjaxconfig = get_config('filter_mathjaxloader', 'mathjaxconfig');
-
-        if (strpos($mathjaxconfig, 'MathJax.Ajax.config.path') !== false) {
-            // Now we need to remove this config again because mathjax 2.7.1 supports the extensions on the CDN.
-            $configtoremove = 'MathJax.Ajax.config.path["Contrib"] = "{wwwroot}/filter/mathjaxloader/contrib";';
-
-            $mathjaxconfig = str_replace($configtoremove, '', $mathjaxconfig);
-
-            set_config('mathjaxconfig', $mathjaxconfig, 'filter_mathjaxloader');
-        }
-
-        upgrade_plugin_savepoint(true, 2017042602, 'filter', 'mathjaxloader');
-    }
-
-    // Automatically generated Moodle v3.3.0 release upgrade line.
-    // Put any upgrade step following this.
-
-    if ($oldversion < 2017091900) {
-
-        $httpsurl = get_config('filter_mathjaxloader', 'httpsurl');
-        if (empty($httpsurl)) {
-            // URL is empty, most likely because of bad upgrade path. See MDL-59780.
-            set_config('httpsurl', 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js', 'filter_mathjaxloader');
-        }
-        upgrade_plugin_savepoint(true, 2017091900, 'filter', 'mathjaxloader');
-    }
-
-    if ($oldversion < 2017100900) {
-        // Update the MathJax CDN URL to the new default if the site has been using default value.
-        $httpsurl = get_config('filter_mathjaxloader', 'httpsurl');
-        if ($httpsurl === 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js') {
-            set_config('httpsurl', 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.2/MathJax.js', 'filter_mathjaxloader');
-        }
-        upgrade_plugin_savepoint(true, 2017100900, 'filter', 'mathjaxloader');
-    }
-
-    if ($oldversion < 2017101200) {
-        // Update default MathJax configuration so that it does not use the Accessible.js config (causes JS errors due to upstream bug).
-        $previousdefault = '
-MathJax.Hub.Config({
-    config: ["Accessible.js", "Safe.js"],
-    errorSettings: { message: ["!"] },
-    skipStartupTypeset: true,
-    messageStyle: "none"
-});
-';
-
-        $newdefault = '
-MathJax.Hub.Config({
-    config: ["default.js", "MMLorHTML.js", "Safe.js"],
-    errorSettings: { message: ["!"] },
-    skipStartupTypeset: true,
-    messageStyle: "none"
-});
-';
-
-        $mathjaxconfig = get_config('filter_mathjaxloader', 'mathjaxconfig');
-
-        if (empty($mathjaxconfig) || filter_mathjaxloader_upgrade_mathjaxconfig_equal($mathjaxconfig, $previousdefault)) {
-            set_config('mathjaxconfig', $newdefault, 'filter_mathjaxloader');
-        }
-
-        upgrade_plugin_savepoint(true, 2017101200, 'filter', 'mathjaxloader');
-    }
-
-    if ($oldversion < 2017102000) {
-        // Re-add Accessible.js (we should not have removed it).
-        $previousdefault = '
-MathJax.Hub.Config({
-    config: ["default.js", "MMLorHTML.js", "Safe.js"],
-    errorSettings: { message: ["!"] },
-    skipStartupTypeset: true,
-    messageStyle: "none"
-});
-';
-        $newdefault = '
-MathJax.Hub.Config({
-    config: ["Accessible.js", "Safe.js"],
-    errorSettings: { message: ["!"] },
-    skipStartupTypeset: true,
-    messageStyle: "none"
-});
-';
-
-        $mathjaxconfig = get_config('filter_mathjaxloader', 'mathjaxconfig');
-
-        if (empty($mathjaxconfig) || filter_mathjaxloader_upgrade_mathjaxconfig_equal($mathjaxconfig, $previousdefault)) {
-            set_config('mathjaxconfig', $newdefault, 'filter_mathjaxloader');
-        }
-
-        upgrade_plugin_savepoint(true, 2017102000, 'filter', 'mathjaxloader');
-    }
-
-    // Automatically generated Moodle v3.4.0 release upgrade line.
-    // Put any upgrade step following this.
-
     // Automatically generated Moodle v3.5.0 release upgrade line.
     // Put any upgrade step following this.
 
diff --git a/filter/mathjaxloader/db/upgradelib.php b/filter/mathjaxloader/db/upgradelib.php
deleted file mode 100644
index 813075698a8..00000000000
--- a/filter/mathjaxloader/db/upgradelib.php
+++ /dev/null
@@ -1,95 +0,0 @@
-<?php
-// This file is part of Moodle - http://moodle.org/
-//
-// Moodle is free software: you can redistribute it and/or modify
-// it under the terms of the GNU General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// Moodle is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-//
-// You should have received a copy of the GNU General Public License
-// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
-
-/**
- * Random functions for mathjax upgrades.
- *
- * @package    filter_mathjaxloader
- * @copyright  2017 Damyon Wiese (damyon@moodle.com)
- * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- */
-
-defined('MOODLE_INTERNAL') || die();
-
-/**
- * This function takes an existing mathjax url and, if it was using the standard mathjax cdn,
- * upgrades it to use the cloudflare matchjax cdn (because the standard one is shutting down).
- * @param string $mathjaxurl - The current url.
- * @param boolean $httponly - Use http instead of https - really only for 3.1 upgrades.
- * @return string The new url.
- */
-function filter_mathjaxloader_upgrade_cdn_cloudflare($mathjaxurl, $httponly = false) {
-    $newcdnurl = $mathjaxurl;
-    $cdnroot = 'https://cdn.mathjax.org/mathjax/';
-    if ($httponly) {
-        $cdnroot = 'http://cdn.mathjax.org/mathjax/';
-    }
-    $usingcdn = strpos($mathjaxurl, $cdnroot) === 0;
-    if ($usingcdn) {
-        $majorversion = substr($mathjaxurl, strlen($cdnroot), 3);
-        $latestversion = '2.7.0';
-        if ($majorversion == '2.6') {
-            $latestversion = '2.6.1';
-        } else if ($majorversion == '2.5') {
-            $latestversion = '2.5.3';
-        }
-
-        $offset = strpos($mathjaxurl, '/', strlen($cdnroot));
-        if ($offset === false) {
-            return $newcdnurl;
-        }
-
-        $endofurl = substr($mathjaxurl, $offset + 1);
-
-        $newcdnbase = 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/';
-        if ($httponly) {
-            $newcdnbase = 'http://cdnjs.cloudflare.com/ajax/libs/mathjax/';
-        }
-
-        $newcdnurl = $newcdnbase . $latestversion . '/' . $endofurl;
-    }
-
-    return $newcdnurl;
-}
-
-/**
- * Compares two values of the 'mathjaxconfig' config option.
- *
- * This is used during the upgrade to see if the two text values of the 'mathjaxconfig' config option should be
- * considered equal of different. The strings are normalized so that EOL characters and whitespace is not significant.
- *
- * @param string $val1 value
- * @param string $val2 value
- * @return bool true if the texts should be considered equals, false otherwise
- */
-function filter_mathjaxloader_upgrade_mathjaxconfig_equal($val1, $val2) {
-
-    $val1lines = preg_split("/[\r\n]/", $val1);
-    $val2lines = preg_split("/[\r\n]/", $val2);
-
-    $val1lines = array_map('trim', $val1lines);
-    $val2lines = array_map('trim', $val2lines);
-
-    $val1lines = array_filter($val1lines, function($value) {
-        return $value !== '';
-    });
-
-    $val2lines = array_filter($val2lines, function($value) {
-        return $value !== '';
-    });
-
-    return (implode(' ', $val1lines) === implode(' ', $val2lines));
-}
diff --git a/filter/mathjaxloader/tests/upgradelib_test.php b/filter/mathjaxloader/tests/upgradelib_test.php
deleted file mode 100644
index 092f293b858..00000000000
--- a/filter/mathjaxloader/tests/upgradelib_test.php
+++ /dev/null
@@ -1,124 +0,0 @@
-<?php
-// This file is part of Moodle - http://moodle.org/
-//
-// Moodle is free software: you can redistribute it and/or modify
-// it under the terms of the GNU General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// Moodle is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-//
-// You should have received a copy of the GNU General Public License
-// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
-
-/**
- * Unit test for the upgrade MathJax code.
- *
- * @package    filter_mathjaxloader
- * @copyright  2017 Damyon Wiese
- * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- */
-
-defined('MOODLE_INTERNAL') || die();
-
-global $CFG;
-require_once($CFG->dirroot . '/filter/mathjaxloader/db/upgradelib.php');
-
-/**
- * Unit test for the upgrade MathJax code.
- *
- * Test the functions in upgradelib.php
- *
- * @copyright  2017 Damyon Wiese
- * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- */
-class filter_mathjax_upgradelib_testcase extends advanced_testcase {
-
-    /**
-     * Tests for {@link filter_mathjaxloader_upgrade_cdn_cloudflare()} function.
-     */
-    public function test_filter_mathjaxloader_upgrade_cdn_cloudflare() {
-        $current = 'https://cdn.mathjax.org/mathjax/2.7-latest/MathJax.js?...';
-        $expected = 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-
-        $current = 'http://cdn.mathjax.org/mathjax/2.7-latest/MathJax.js?...';
-        $expected = 'http://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current, true));
-
-        $current = 'http://cdn.mathjax.org/mathjax/2.7-latest/MathJax.js?...';
-        $expected = 'http://cdn.mathjax.org/mathjax/2.7-latest/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current, false));
-
-        $current = 'https://cdn.mathjax.org/mathjax/2.7-latest/MathJax.js?...';
-        $expected = 'https://cdn.mathjax.org/mathjax/2.7-latest/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current, true));
-
-        $current = 'https://cdn.mathjax.org/mathjax/2.6-latest/MathJax.js?...';
-        $expected = 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.6.1/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-
-        $current = 'https://cdn.mathjax.org/mathjax/2.5-latest/MathJax.js?...';
-        $expected = 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.5.3/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-
-        // Dont touch non https links.
-        $current = 'http://cdn.mathjax.org/mathjax/2.5-latest/MathJax.js?...';
-        $expected = 'http://cdn.mathjax.org/mathjax/2.5-latest/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-
-        // Dont touch non local links.
-        $current = 'https://mylocalmirror/mathjax/2.7-latest/MathJax.js?...';
-        $expected = 'https://mylocalmirror/mathjax/2.7-latest/MathJax.js?...';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-
-        // Try some unexpected things.
-        $current = '';
-        $expected = '';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-
-        // Try some unexpected things.
-        $current = 'https://cdn.mathjax.org/mathjax/2.7-latest/MathJax.js';
-        $expected = 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-
-        // Try some unexpected things.
-        $current = 'https://cdn.mathjax.org/mathjax/2.7-latest';
-        $expected = 'https://cdn.mathjax.org/mathjax/2.7-latest';
-        $this->assertEquals($expected, filter_mathjaxloader_upgrade_cdn_cloudflare($current));
-    }
-
-    /**
-     * Tests for {@link filter_mathjaxloader_upgrade_mathjaxconfig_equal()} function.
-     */
-    public function test_filter_mathjaxloader_upgrade_mathjaxconfig_equal() {
-
-        $val1 = '';
-        $val2 = "\n \r \r\n \t    ";
-        $this->assertTrue(filter_mathjaxloader_upgrade_mathjaxconfig_equal($val1, $val2));
-
-        $val1 = '0';
-        $val2 = '';
-        $this->assertFalse(filter_mathjaxloader_upgrade_mathjaxconfig_equal($val1, $val2));
-
-        $val1 = 'Hello Unittest, my old friend    '.PHP_EOL."I've come to play with you again  \r\n\r\n  \t ";
-        $val2 = '   Hello Unittest, my old friend '."\r\n\r\n"."  I've come to play with you again \n\n\n  ";
-        $this->assertTrue(filter_mathjaxloader_upgrade_mathjaxconfig_equal($val1, $val2));
-
-        $val1 = "\n".'MathJax.Hub.Config({'."\n".'    config: ["Accessible.js", "Safe.js"]'."\n".'});'."\n";
-        $val2 = 'MathJax.Hub.Config({'."\r".'config: ["Accessible.js", "Safe.js"]'."\r".'});';
-        $this->assertTrue(filter_mathjaxloader_upgrade_mathjaxconfig_equal($val1, $val2));
-
-        $val1 = "\r\n\t".'MathJax.Hub.Config({'."\r\n\t".' config: ["Accessible.js", "Safe.js"]'."\r\n".'});  '."\r\n\r\n";
-        $val2 = 'MathJax.Hub.Config({'."\n".'config: ["Accessible.js", "Safe.js"]'."\r".'});';
-        $this->assertTrue(filter_mathjaxloader_upgrade_mathjaxconfig_equal($val1, $val2));
-
-        $val2 = 'MathJax.Hub.Config({'."\n".'config: ["Significant.js"]'."\n".'});';
-        $val2 = 'MathJax.Hub.Config({'."\n".'config: ["Signi ficant.js", "Safe.js"]'."\n".'});';
-        $this->assertFalse(filter_mathjaxloader_upgrade_mathjaxconfig_equal($val1, $val2));
-    }
-}
-
diff --git a/filter/upgrade.txt b/filter/upgrade.txt
index 3ccfc6e333f..dfccf3f5f4e 100644
--- a/filter/upgrade.txt
+++ b/filter/upgrade.txt
@@ -1,6 +1,12 @@
 This file describes API changes in core filter API and plugins,
 information provided here is intended especially for developers.
 
+=== 3.9 ===
+
+* The following functions, previously used (exclusively) by upgrade steps are not available anymore because of the upgrade cleanup performed for this version. See MDL-65809 for more info:
+    - filter_mathjaxloader_upgrade_cdn_cloudflare()
+    - filter_mathjaxloader_upgrade_mathjaxconfig_equal()
+
 === 3.6 ===
 
 * Although there is no API change that require you to update your filter,