logind-user: don't say "user X logged out" in user_finalize

logind-user: don't say "user X logged out" in user_finalize

"Logging out" is something done by the human user. When we stop
tracking/GC a User object, let's use a more generic phrase in case
the specific User doesn't have human users (i.e. "user" class sessions)
at all. Eventually we want something like #2900, and log this
when all user class sessions log out and we're lingering again I think.