shell: cleanup DesktopView screen change reactions
DesktopView's screen should only change as a result of an explicit call, we don't need to track.
We don't need two member variables to track old and new screens if the code gets shuffled.
DesktopView's screen should only change as a result of an explicit call, we don't need to track.
We don't need two member variables to track old and new screens if the code gets shuffled.