MDL-49008 lang: Revert unnecessary rename warning

This was failing unit tests because it does not check for the presence of
the source directory first. If there is no source directory, it cannot be
moved.

lib/componentlib.class.php

@@ -326,10 +326,7 @@ class component_installer {
         @remove_dir($destinationcomponent.'_old');     // Deleting a possible old version.
 
         // Moving to a safe place.
-        $moveresult = @rename($destinationcomponent, $destinationcomponent.'_old');
-        if (!$moveresult) {
-            debugging("Failed to rename {$destinationcomponent} to {$destinationcomponent}_old while installing a language");
-        }
+        @rename($destinationcomponent, $destinationcomponent.'_old');
 
     /// Unzip new version
         if (!unzip_file($zipfile, $destinationdir, false)) {