MDL-59823 users: Enrol bulk op course instance

The commit message above was my best attempt at meeting the very short restrictions on commit message first lines.

What it needed to say was: "Only show bulk enrolment operations for enrolment methods that have an instance in the course"

enrol/locallib.php

@@ -554,7 +554,7 @@ class course_enrolment_manager {
     }
 
     /**
-     * Gets all of the enrolment plugins that are active for this course.
+     * Gets all of the enrolment plugins that are available for this course.
      *
      * @param bool $onlyenabled return only enabled enrol plugins
      * @return array

user/index.php

@@ -254,8 +254,14 @@ if ($bulkoperations) {
     }
 
     if ($context->id != $frontpagectx->id) {
-        $plugins = $manager->get_enrolment_plugins();
-        foreach ($plugins as $plugin) {
+        $instances = $manager->get_enrolment_instances();
+        $plugins = $manager->get_enrolment_plugins(false);
+        foreach ($instances as $key => $instance) {
+            if (!isset($plugins[$instance->enrol])) {
+                // Weird, some broken stuff in plugin.
+                continue;
+            }
+            $plugin = $plugins[$instance->enrol];
             $bulkoperations = $plugin->get_bulk_operations($manager);
 
             $pluginoptions = [];