ffmpeg: drop useless framerate assignments

If the input stream framerate is known, it will be configured on the
relevant filtergraph input and get propagated to the output stream in
the above line. That makes these assignments redundant.

fftools/ffmpeg.c

@@ -3293,10 +3293,6 @@ static int init_output_stream_encode(OutputStream *ost, AVFrame *frame)
     if (enc_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {
         if (!ost->frame_rate.num)
             ost->frame_rate = av_buffersink_get_frame_rate(ost->filter->filter);
-        if (ist && !ost->frame_rate.num)
-            ost->frame_rate = ist->framerate;
-        if (ist && !ost->frame_rate.num)
-            ost->frame_rate = ist->st->r_frame_rate;
         if (ist && !ost->frame_rate.num && !ost->max_frame_rate.num) {
             ost->frame_rate = (AVRational){25, 1};
             av_log(NULL, AV_LOG_WARNING,