output_event_commit: Remove committed and buffer

The newly introduced state struct can be used to retrieve this.

include/wlr/types/wlr_output.h

@@ -218,9 +218,7 @@ struct wlr_output_event_precommit {
 
 struct wlr_output_event_commit {
 	struct wlr_output *output;
-	uint32_t committed; // bitmask of enum wlr_output_state_field
 	struct timespec *when;
-	struct wlr_buffer *buffer; // NULL if no buffer is committed
 	const struct wlr_output_state *state;
 };