remove depracated function

includes/utilities.inc

@@ -12,6 +12,7 @@
  */
 
 use Drupal\Component\Utility\Xss;
+use Drupal\Component\Utility\Html;
 
 function upei_roblib_ill_check_arr_item(&$value, $key) {
   if (is_array($value)) {
@@ -95,7 +96,7 @@ function upei_roblib_ill_get_request_variable($variable) {
   if (($variable == 'genre' && !empty($_REQUEST[$variable])) && $_REQUEST[$variable] == 'bookitem') {
     return 'chapter';
   }
-  return isset($_REQUEST[$variable]) ? check_plain($_REQUEST[$variable]) : '';
+  return isset($_REQUEST[$variable]) ? Html::escape($_REQUEST[$variable]) : '';
 }