avformat: do not require frame_size in avformat_find_stream_info() for MP1/2/3

It was only needed to avoid a bad time base (and thus non-monotone timestamps)
for stream copy to avi.

libavformat/utils.c

@@ -2019,9 +2019,6 @@ static int has_codec_parameters(AVCodecContext *avctx)
     case AVMEDIA_TYPE_AUDIO:
         val = avctx->sample_rate && avctx->channels && avctx->sample_fmt != AV_SAMPLE_FMT_NONE;
         if (!avctx->frame_size &&
-             avctx->codec_id == CODEC_ID_MP1 ||
-             avctx->codec_id == CODEC_ID_MP2 ||
-             avctx->codec_id == CODEC_ID_MP3 ||
              avctx->codec_id == CODEC_ID_CELT))
             return 0;
         break;