remove obsolete check of c->mon in fullscreennotify()

since 19a8a095eb it's checked in setfullscreen()

dwl.c

@@ -1246,14 +1246,7 @@ void
 fullscreennotify(struct wl_listener *listener, void *data)
 {
 	Client *c = wl_container_of(listener, c, fullscreen);
-	int fullscreen = client_wants_fullscreen(c);
-
-	if (!c->mon) {
-		/* if the client is not mapped yet, let mapnotify() call setfullscreen() */
-		c->isfullscreen = fullscreen;
-		return;
-	}
-	setfullscreen(c, fullscreen);
+	setfullscreen(c, client_wants_fullscreen(c));
 }
 
 void