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/amr.c

@@ -153,7 +153,6 @@ static int amr_read_packet(AVFormatContext *s, AVPacket *pkt)
     read              = avio_read(s->pb, pkt->data + 1, size - 1);
 
     if (read != size - 1) {
-        av_packet_unref(pkt);
         if (read < 0)
             return read;
         return AVERROR(EIO);