demux_lavf: remove fix_editlists hack for mp4

Remove this "hack" from 2017 which disabled `advanced_editlist` while
demuxing mov/mp4. See: b7b12c3 as well
as b86a231

At present, advanced edit list support seems to be mature enough that it
doesn't need to be disabled by us and disabling it seems to break more
files based on testing with `elist` files in FFmpeg's FATE suite.

demux/demux_lavf.c

@@ -146,7 +146,6 @@ struct format_hack {
     // segment, with e.g. HLS, player knows about the playlist main file only).
     bool clear_filepos : 1;
     bool linearize_audio_ts : 1;// compensate timestamp resets (audio only)
-    bool fix_editlists : 1;
     bool is_network : 1;
     bool no_seek : 1;
     bool no_pcm_seek : 1;
@@ -175,8 +174,7 @@ static const struct format_hack format_hacks[] = {
     {"mxf", .use_stream_ids = true},
     {"avi", .use_stream_ids = true},
     {"asf", .use_stream_ids = true},
-    {"mp4", .skipinfo = true, .fix_editlists = true, .no_pcm_seek = true,
-            .use_stream_ids = true},
+    {"mp4", .skipinfo = true, .no_pcm_seek = true, .use_stream_ids = true},
     {"matroska", .skipinfo = true, .no_pcm_seek = true, .use_stream_ids = true},
 
     {"v4l2", .no_seek = true},
@@ -1065,9 +1063,6 @@ static int demux_open_lavf(demuxer_t *demuxer, enum demux_check check)
 
     guess_and_set_vobsub_name(demuxer, &dopts);
 
-    if (priv->format_hack.fix_editlists)
-        av_dict_set(&dopts, "advanced_editlist", "0", 0);
-
     avfc->interrupt_callback = (AVIOInterruptCB){
         .callback = interrupt_cb,
         .opaque = demuxer,
@@ -1267,8 +1262,6 @@ static bool demux_lavf_read_packet(struct demuxer *demux,
     dp->duration = pkt->duration * av_q2d(st->time_base);
     dp->pos = pkt->pos;
     dp->keyframe = pkt->flags & AV_PKT_FLAG_KEY;
-    if (pkt->flags & AV_PKT_FLAG_DISCARD)
-        MP_ERR(demux, "Edit lists are not correctly supported (FFmpeg issue).\n");
     av_packet_unref(pkt);
 
     if (priv->format_hack.clear_filepos)