wayland/idle-inhibit: Handle actor going away
There were some fixes to how to handle actor going away and being recreated, but it didn't go all the way. This is the last step that sholud have been.
Fixes: a3c62bf8 ("wayland/idle-inhibit: Add state tracking to fix races") Related: https://bugzilla.redhat.com/show_bug.cgi?id=2238785