doc/examples/mux: remove nop

Found through code review related to CID1604493 Overflowed constant

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/examples/mux.c

@@ -347,8 +347,7 @@ static int write_audio_frame(AVFormatContext *oc, OutputStream *ost)
     if (frame) {
         /* convert samples from native format to destination codec format, using the resampler */
         /* compute destination number of samples */
-        dst_nb_samples = av_rescale_rnd(swr_get_delay(ost->swr_ctx, c->sample_rate) + frame->nb_samples,
-                                        c->sample_rate, c->sample_rate, AV_ROUND_UP);
+        dst_nb_samples = swr_get_delay(ost->swr_ctx, c->sample_rate) + frame->nb_samples;
         av_assert0(dst_nb_samples == frame->nb_samples);
 
         /* when we pass a frame to the encoder, it may keep a reference to it