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/dml/tests/pgsql_native_moodle_database_test.php

@@ -89,7 +89,6 @@ class pgsql_native_moodle_database_test extends \advanced_testcase {
         global $DB;
         $reflector = new ReflectionClass($DB);
         $property = $reflector->getProperty('inorequaluniqueindex');
-        $property->setAccessible(true);
         return (int) $property->getValue($DB);
     }
 
@@ -390,7 +389,6 @@ class pgsql_native_moodle_database_test extends \advanced_testcase {
 
         $reflector = new ReflectionClass($db2);
         $rp = $reflector->getProperty('pgsql');
-        $rp->setAccessible(true);
         return $rp->getValue($db2);
     }