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/icodec.c

@@ -185,7 +185,6 @@ static int read_packet(AVFormatContext *s, AVPacket *pkt)
         bytestream_put_le32(&buf, 0);
 
         if ((ret = avio_read(pb, buf, image->size)) != image->size) {
-            av_packet_unref(pkt);
             return ret < 0 ? ret : AVERROR_INVALIDDATA;
         }