yum-cron is part of the main yum package now, so the standalone version needs to be retired - see bug 881715. This is for F18 and devel: it has already been done for el6 (was bug 749394).

Did the "fedpkg retire" steps. And unable to update the fedora package database by clickign "retire package", as it's already marked "depreciated" for those releases, so that box isn't in the web form.