update_chroot: fix transition to new os-release location

Previously /etc/os-release was installed both by set_lsb_release and
the baselayout package. Now it is only installed by set_lsb_release but
when baselayout is upgraded it removes /etc/os-release. So the first
update_chroot works but the second detects the chroot's version
incorrectly and tries to apply the one time updates in this directory.
Both of them are very old so we can just delete them. The second run
will now fix up /etc/os-release and we can all move on and be happy.