Dropping xmldb_dbg($message). Now it has been replaced by a new cleaner

debug system, with XMLDB hook for debug enabled by the creation of one
function called: xmldb_debug($message, $object), currently present in
lib/datalib.php MDL-7261

lib/ddllib.php

@@ -1167,8 +1167,4 @@ function change_db_encoding() {
     }
 }
 
-function xmldb_dbg($message) {
-    error_log($message);
-}
-
 ?>