Disable DVD and BD menu support (to be removed)

DVD/BD menu support never worked right, and are a pain to maintain. In
particular, DVD menus never actually worked correctly, because
highlights were not rendered correctly. Fixing this requires major
effort, which I'm not interested to spend.

Most importantly, the requirement to switch streams without losing the
DVD/BD state caused major weirdness in the playback core. It was
implemented by somehow syncing the playback state to the DVD/BD
implementation (in stream_dvdnav.c etc.), and then reloading the demuxer
without destroying and recreating the stream. This caused a bunch of
special-cases which I'm looking forward to remove.

For now, don't just remove everything related to menu support and just
disable it. If someone volunteers, it can be restored (i.e. rewritten)
in a reasonable way. If nobody volunteers soon, it goes.

stream/stream_dvdnav.c

@@ -781,6 +781,8 @@ static int open_s(stream_t *stream)
             return STREAM_UNSUPPORTED;
         }
     } else {
+        MP_FATAL(stream, "DVD menu support has been removed.\n");
+        return STREAM_ERROR;
         if (dvdnav_menu_call(priv->dvdnav, DVD_MENU_Root) != DVDNAV_STATUS_OK)
             dvdnav_menu_call(priv->dvdnav, DVD_MENU_Title);
     }