Ignore latency-updates while removing tracks.
remove_tracks() calls disconnect_all() which can trigger the backend
to perform a latency-recompute in a different thread (process thread).
That calls Session::update_latency() which iterates over all routes
including the one(s) to be deleted.
At the same time disconnect_all() may propagate Port::PostDisconnect()
leading to a lock contention.
(no crash just a lot of unnecessary work. remove_routes() calls
update_latency_compensation() which triggers a recompute if needed)
4c40fe8d04