MDL-81581 phpunit: Move multiple assert_same_xml() to common one

question/format/xml/tests/xmlformat_test.php

@@ -47,11 +47,6 @@ require_once($CFG->dirroot . '/question/engine/tests/helpers.php');
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class xmlformat_test extends \question_testcase {
-    public function assert_same_xml($expectedxml, $xml) {
-        $this->assertEquals(str_replace("\r\n", "\n", $expectedxml),
-                str_replace("\r\n", "\n", $xml));
-    }
-
     public function make_test_question() {
         global $USER;
         $q = new \stdClass();