output: require commit after hardware cursor update

Up until now only the DRM backend required an output commit after
updating the cursor. Unify this for all backends, because:

- Screen capture can now catch cursor updates listening for output
  commits
- In the future we want to make the cursor a regular wlr_output_layer,
  which would need an output commit to be updated anyways

backend/drm/drm.c

@@ -1162,7 +1162,6 @@ static bool drm_connector_set_cursor(struct wlr_output *output,
 		conn->cursor_height = buffer->height;
 	}
 
-	wlr_output_update_needs_frame(output);
 	return true;
 }
 
@@ -1192,7 +1191,6 @@ static bool drm_connector_move_cursor(struct wlr_output *output,
 	conn->cursor_x = box.x;
 	conn->cursor_y = box.y;
 
-	wlr_output_update_needs_frame(output);
 	return true;
 }