Clear stored root window id when shutting down X
Clear stored root window id when shutting down X

Currently e_comp_util_has_x() will still return true after the X
machinery is shut down - this can lead to crashes on logout under
wayland when xwayland apps are running.  Clearing the root window
id resolves this.

@ref T5593

tasn/enlightenment,tasn/enlightenment,tasn/enlightenment