x11: allow display sync modes to report no visibility

When this was originally implemented, I lazily skipped the optimization
when using display sync because mpv would rip through all the frames
without waiting since there was no blocking. With the previous commits,
we now fall back on the audio sync logic when the window is not visible,
so the extra condition can be removed.

video/out/x11_common.c

@@ -2071,10 +2071,7 @@ bool vo_x11_check_visible(struct vo *vo)
 {
     struct vo_x11_state *x11 = vo->x11;
     struct mp_vo_opts *opts = x11->opts;
-
-    bool render = !x11->hidden || opts->force_render ||
-                  VS_IS_DISP(opts->video_sync);
-    return render;
+    return !x11->hidden || opts->force_render;
 }
 
 static void vo_x11_set_input_region(struct vo *vo, bool passthrough)