refactor: remove unneeded methods

Author: kenjis

system/Test/Mock/MockConnection.php

@@ -240,14 +240,4 @@ protected function _transRollback(): bool
     {
         return true;
     }
-
-    protected function _disableForeignKeyChecks()
-    {
-        return '';
-    }
-
-    protected function _enableForeignKeyChecks()
-    {
-        return '';
-    }
 }