Remove decoration event listeners on destroynotify

When destroynotify doesn't clean up these listeners it causes a crash once the cleanup of the decoration is triggered

Thanks to kennylevinsen - https://codeberg.org/dwl/dwl/issues/1205#issuecomment-22424401

dwl.c

@@ -1348,6 +1348,10 @@ destroynotify(struct wl_listener *listener, void *data)
 		wl_list_remove(&c->map.link);
 		wl_list_remove(&c->unmap.link);
 		wl_list_remove(&c->maximize.link);
+		if (c->decoration) {
+			wl_list_remove(&c->set_decoration_mode.link);
+			wl_list_remove(&c->destroy_decoration.link);
+		}
 	}
 	free(c);
 }