MDL-75952 general: Since php81, refection->setAccessible() is no-op

Refereces:
- https://wiki.php.net/rfc/make-reflection-setaccessible-no-op
- https://www.php.net/manual/en/reflectionproperty.setaccessible.php
- https://www.php.net/manual/en/reflectionmethod.setaccessible.php

As of PHP 8.1.0, calling this method has no effect; all methods are
invokable by default. So, let's remove all uses from core, they are
no-op.

lib/tests/completionlib_test.php

@@ -966,7 +966,6 @@ class completionlib_test extends advanced_testcase {
         $completioninfo = new completion_info($this->course);
 
         $method = new ReflectionMethod("completion_info", "get_other_cm_completion_data");
-        $method->setAccessible(true);
 
         // Check that fetching data for a module with custom completion provides its info.
         $choicecompletiondata = $method->invoke($completioninfo, $cmchoice, $user->id);
@@ -1813,7 +1812,6 @@ class completionlib_test extends advanced_testcase {
 
         // We're testing a private method, so we need to setup reflector magic.
         $method = new ReflectionMethod($ccompletion, '_save');
-        $method->setAccessible(true); // Allow accessing of private method.
         $completionid = $method->invoke($ccompletion);
         $completions = $DB->get_records('course_completions');
         $this->assertEquals(count($completions), 1);
@@ -1821,7 +1819,6 @@ class completionlib_test extends advanced_testcase {
 
         $ccompletion->id = 0;
         $method = new ReflectionMethod($ccompletion, '_save');
-        $method->setAccessible(true); // Allow accessing of private method.
         $completionid = $method->invoke($ccompletion);
         $this->assertDebuggingCalled('Can not update data object, no id!');
         $this->assertNull($completionid);