Hi!
We need to clean up old MediaWiki messages translations on be-x-old Wikipedia. deleteDefaultMessages.php looks as perfect candidate for this job. However last changes from MediaWiki_default were made in 2007.
Is this code still functional? If so, I think will be good idea to run it on all WMF wikis, especially those which had long history of translation of MediaWiki messages (before translatewiki.net).
Eugene.