ivi-shell: Remove the compositor destory listener from list during de-init

During de-init ensure removal of compositor destroy notification
from list. Otherwise a dongling pointer is left behind which will
affect other plugins.

Signed-off-by: Harsha M M <harsha.manjulamallikarjun@in.bosch.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>