pointer: store the output instead of its name

In cases where the value is actually valid, the input device lives
just as long as the output, so it's easier to provide the output itself
instead for making a compositor find it by the name.

types/wlr_pointer.c

@@ -36,6 +36,4 @@ void wlr_pointer_init(struct wlr_pointer *pointer,
 
 void wlr_pointer_finish(struct wlr_pointer *pointer) {
 	wlr_input_device_finish(&pointer->base);
-
-	free(pointer->output_name);
 }