MDL-69918 core: Update uses of legacy form change checker

admin/settings.php

@@ -148,13 +148,8 @@ if (empty($SITE->fullname)) {
     echo $OUTPUT->render_from_template('core_admin/settings', $context);
 }
 
-$PAGE->requires->yui_module('moodle-core-formchangechecker',
-        'M.core_formchangechecker.init',
-        array(array(
-            'formid' => 'adminsettings'
-        ))
-);
-$PAGE->requires->string_for_js('changesmadereallygoaway', 'moodle');
+// Add the form change checker.
+$PAGE->requires->js_call_amd('core_form/changechecker', 'watchFormById', ['adminsettings']);
 
 if ($settingspage->has_dependencies()) {
     $opts = [