compositor-wayland: actually free parent_output

I could not find anywhere where struct parent_output was freed, so
apparently we were leaking it.

Check against wayland_backend_register_output() and add the missing
clean-up: removal from the parent output list, and free().

registry_handle_global_remove() also needs fixing to use a safer loop,
because now we are actually removing the list item.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Acked-by: Daniel Stone <daniels@collabora.com>
1 file changed