Delete unneeded mount-athena.in

We stopped shipping this as of 2.0.46, and should have removed
it in c70dd6f.
Fix /sys bind-mount; fix dbus inhibitor

- We need to recursively mount /sys, because of things like
  /sys/fs/cgroup in the systemd world. (Trac: #1499)
- 90debathena-reactivate should, at startup time, kill the
  dbus inhibitor file if it exists (it can be present due to
  stale chroots being ended at reboot time by the init.d script
  (Trac: #1497)
Add setup.d to umount -l /afs

Lazily umount /afs inside the chroot, before attempting the
normal umount.  gvfs can leave something hanging around such that
a normal umount returns EBUSY.  (Trac: #1500)
Release 2.0.47

Release 2.0.47, containing the fixes for Trac: #1497, #1499
and #1500