This properly takes care of removing any of the views being added into
different layers upon shell destruction. Aggregates the shell_surface
destruction into one place to make things much more clearer. Keep the
animation part only the weston_desktop_surface destruction rather than
doing it at shutdown.
Fixes#509.
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
d25d63e692