screenShield: Do not save lock state on wayland

We keep track of the lock state and restore it on startup to prevent a crash from bypassing the screen lock. However on wayland, a crash doesn't result in gnome-session restarting gnome-shell, but brings down the entire session - that is, restoring the lock state does not actually protect the existing session in that case, but forces the user to authenticate twice in order to start the next session. This is clearly not helpful, so avoid this by not saving the state when running as wayland compositor.