ffmpeg: remove "has_b_frames" backpassing

It seems working without this now for the files i tested it with, if this causes
a regression, dont hesitate to put the line back or open a ticket or fix (if possible)
the parser
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -1859,7 +1859,10 @@ static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output)
     ret = avcodec_decode_video2(ist->dec_ctx,
                                 decoded_frame, got_output, pkt);
     update_benchmark("decode_video %d.%d", ist->file_index, ist->st->index);
-    ist->st->codec->has_b_frames = ist->dec_ctx->has_b_frames; //FIXME remove this once all AVParsers set it correctly
+
+    // The following line may be required in some cases where there is no parser
+    // or the parser does not has_b_frames correctly
+//     ist->st->codec->has_b_frames = ist->dec_ctx->has_b_frames;
 
     if (*got_output || ret<0 || pkt->size)
         decode_error_stat[ret<0] ++;