avformat: Remove unnecessary av_packet_unref()

Since bae8844e the packet will always be unreferenced when a demuxer
returns an error, so that a lot of calls to av_packet_unref() in lots of
demuxers are now redundant and can be removed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>

libavformat/mpc.c

@@ -169,7 +169,6 @@ static int mpc_read_packet(AVFormatContext *s, AVPacket *pkt)
     if(c->curbits)
         avio_seek(s->pb, -4, SEEK_CUR);
     if(ret < size){
-        av_packet_unref(pkt);
         return ret < 0 ? ret : AVERROR(EIO);
     }
     pkt->size = ret + 4;