win: merge win::pending_updates and win::flags

These two flags are intended for subtly different things. I can probably
justify the distinction, but it's definitely difficult to explain. And
there is no obvious benefits to keep them separate.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/event.c

@@ -287,7 +287,7 @@ static inline void ev_map_notify(session_t *ps, xcb_map_notify_event_t *ev) {
 		return;
 	}
 
-	win_queue_update(w, WIN_UPDATE_MAP);
+	win_set_flags(w, WIN_FLAGS_MAPPED);
 
 	// FocusIn/Out may be ignored when the window is unmapped, so we must
 	// recheck focus here