PV-5: Change validating schema

Author: Dmitry Kologrivov

lib/internal/Magento/Framework/Config/Dom.php

@@ -274,11 +274,7 @@ public static function validateDomDocument(
         $schema = self::$urnResolver->getRealPath($schema);
         libxml_use_internal_errors(true);
         try {
-            if (file_exists($schema)) {
-                $result = $dom->schemaValidate($schema);
-            } else {
-                $result = $dom->schemaValidateSource($schema);
-            }
+            $result = $dom->schemaValidate($schema);
             $errors = [];
             if (!$result) {
                 $validationErrors = libxml_get_errors();