Revert "Merge branch 'avoid_shutdown_failure_v2' into 'master'"

This reverts merge request !55 (merged) the justification for !55 (merged) was indeed incorrect, and thinking about it now, dropping attach-to-session means shutdown messages won't be broadcast to all serial consoles if there is more than one, now, which is a somewhat useful feature some users might rely on. So it might make sense to revert,