fftools/ffmpeg_filter: drop a block commented out since 2012

Since the option it relates to is deprecated, it is highly unlikely to
become useful.

fftools/ffmpeg_filter.c

@@ -902,19 +902,6 @@ static int configure_input_audio_filter(FilterGraph *fg, InputFilter *ifilter,
         AUTO_INSERT_FILTER_INPUT("-async", "aresample", args);
     }
 
-//     if (ost->audio_channels_mapped) {
-//         int i;
-//         AVBPrint pan_buf;
-//         av_bprint_init(&pan_buf, 256, 8192);
-//         av_bprintf(&pan_buf, "0x%"PRIx64,
-//                    av_get_default_channel_layout(ost->audio_channels_mapped));
-//         for (i = 0; i < ost->audio_channels_mapped; i++)
-//             if (ost->audio_channels_map[i] != -1)
-//                 av_bprintf(&pan_buf, ":c%d=c%d", i, ost->audio_channels_map[i]);
-//         AUTO_INSERT_FILTER_INPUT("-map_channel", "pan", pan_buf.str);
-//         av_bprint_finalize(&pan_buf, NULL);
-//     }
-
     snprintf(name, sizeof(name), "trim for input stream %d:%d",
              ist->file_index, ist->st->index);
     if (copy_ts) {