tests: fix test-shell init error path

This was forgetting to remove the compositor destroy listener if init failed,
which would lead to use-after-free on compositor tear-down. Found by
inspection.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

tests/weston-test-desktop-shell.c

@@ -224,6 +224,7 @@ out_surface:
 	weston_surface_destroy(dts->background_surface);
 
 out_free:
+	wl_list_remove(&dts->compositor_destroy_listener.link);
 	free(dts);
 
 	return -1;