Fix stress issue when keeping ctrl-d pressed when deleting 10 or so

Fix stress issue when keeping ctrl-d pressed when deleting 10 or so
windows.  It comes down to events being tossed by the x server causing
dead windows to not be removed from the managed list.  Apply a huge hammer
by removing the dead windows from the list when counting them for stacking
purposes.

Undo some previous added synchronization code that was not necessary but
had given me the illusion of serializing some things.