flvenc: dont call avio_flush() unconditional

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/flvenc.c

@@ -569,7 +569,6 @@ static int flv_write_packet(AVFormatContext *s, AVPacket *pkt)
                               pkt->pts + flv->delay + pkt->duration);
     }
 
-    avio_flush(pb);
     av_free(data);
 
     return pb->error;