don't NULL-check output when it can't be

`output` here is the `pos` argument of `wl_list_for_each`, which means
it is always assigned a return value of `wl_container_of`; this in
turn means that it is never NULL.

checking against NULL here just confuses static analysis and readers

src/output.c

@@ -392,10 +392,8 @@ do_output_layout_change(struct server *server)
 		struct output *output;
 
 		wl_list_for_each(output, &server->outputs, link) {
-			if (output) {
 			layers_arrange(output);
 		}
-		}
 		output_update_for_layout_change(server);
 	}
 }