Revert "avformat/dashenc: use AVStream timebase when computing missing bitrate"

This reverts commit 2a9ffd89fc as duration is always in AV_TIME_BASE units

libavformat/dashenc.c

@@ -1960,7 +1960,7 @@ static int dash_flush(AVFormatContext *s, int final, int stream)
 
         if (!os->bit_rate) {
             // calculate average bitrate of first segment
-            int64_t bitrate = (int64_t) range_length * 8 * (c->use_timeline ? os->ctx->streams[0]->time_base.den : AV_TIME_BASE) / duration;
+            int64_t bitrate = (int64_t) range_length * 8 * AV_TIME_BASE / duration;
             if (bitrate >= 0)
                 os->bit_rate = bitrate;
         }