Delete maintenance/deleteRevision.php

It hasn't been updated properly since 2006 so many fields aren't being
copied to the archive table. Tim suggests it'd be best to just delete it
and, if someone needs the ability to delete or revdel revisions from the
command line, properly abstract out the deletion code instead of
duplicating it.

Change-Id: I400b8ac30b31802e7dd9f6e4d0ec10918eba0183