demux_lavf: remove "internet radio hack"

It appears this is not needed anymore. ffmpeg can handle "chained" ogg
files fine. These can be created with "cat file1.ogg file2.ogg > chained.ogg",
and are similar (or equal) to some internet radio streams. Apparently
ffmpeg used to add new tracks when crossing boundaries in chained files,
and the hack in demux_lavf.c handled this. At some later point, ffmpeg's
ogg demuxer was improved, and stopped adding new tracks as long as the
codec doesn't change.

Since the hack in demux_lavf.c was hardcoded to Vorbis (i.e. only active
if the new and old track were both Vorbis), it's dead code, and we can
remove it. I couldn't find any stream that triggered this hack, or fails
without it.

Firefox had a similar issue, and its bug tracker makes a good reference:

    https://bugzilla.mozilla.org/show_bug.cgi?id=455165

NOTE: this doesn't update metadata on track changes anymore.

demux/demux_lavf.c

@@ -79,7 +79,6 @@ typedef struct lavf_priv {
     int sstreams[MAX_S_STREAMS];
     int cur_program;
     int nb_streams_last;
-    bool internet_radio_hack;
     bool use_dts;
     bool seek_by_bytes;
     int bitrate;
@@ -744,42 +743,6 @@ static demuxer_t *demux_open_lavf(demuxer_t *demuxer)
     return demuxer;
 }
 
-static void check_internet_radio_hack(struct demuxer *demuxer)
-{
-    struct lavf_priv *priv = demuxer->priv;
-    struct AVFormatContext *avfc = priv->avfc;
-
-    if (!matches_avinputformat_name(priv, "ogg"))
-        return;
-    if (priv->nb_streams_last == avfc->nb_streams)
-        return;
-    if (avfc->nb_streams - priv->nb_streams_last == 1
-        && priv->video_streams == 0 && priv->sub_streams == 0
-        && demuxer->a_streams[priv->audio_streams - 1]->format == 0x566f // vorbis
-        && (priv->audio_streams == 2 || priv->internet_radio_hack)
-        && demuxer->a_streams[0]->format == 0x566f) {
-        // extradata match could be checked but would require parsing
-        // headers, as the comment section will vary
-        if (!priv->internet_radio_hack) {
-            mp_msg(MSGT_DEMUX, MSGL_V,
-                   "[lavf] enabling internet ogg radio hack\n");
-        }
-        priv->internet_radio_hack = true;
-        // use new per-track metadata as global metadata
-        AVDictionaryEntry *t = NULL;
-        AVStream *stream = avfc->streams[avfc->nb_streams - 1];
-        while ((t = av_dict_get(stream->metadata, "", t,
-                                AV_DICT_IGNORE_SUFFIX)))
-            demux_info_add(demuxer, t->key, t->value);
-    } else {
-        if (priv->internet_radio_hack)
-            mp_tmsg(MSGT_DEMUX, MSGL_WARN, "[lavf] Internet radio ogg hack "
-                    "was enabled, but stream characteristics changed.\n"
-                    "This may or may not work.\n");
-        priv->internet_radio_hack = false;
-    }
-}
-
 static int destroy_avpacket(void *pkt)
 {
     av_free_packet(pkt);
@@ -806,7 +769,6 @@ static int demux_lavf_fill_buffer(demuxer_t *demux, demux_stream_t *dsds)
     // handle any new streams that might have been added
     for (id = priv->nb_streams_last; id < priv->avfc->nb_streams; id++)
         handle_stream(demux, priv->avfc, id);
-    check_internet_radio_hack(demux);
 
     priv->nb_streams_last = priv->avfc->nb_streams;
 
@@ -820,7 +782,7 @@ static int demux_lavf_fill_buffer(demuxer_t *demux, demux_stream_t *dsds)
         demux->sub->id = id;
     }
 
-    if (id == demux->audio->id || priv->internet_radio_hack) {
+    if (id == demux->audio->id) {
         // audio
         ds = demux->audio;
         if (!ds->sh) {