rtpenc_chain: Don't copy the time_base back to the caller

If required, the caller can do this itself. ff_write_chained rescales
timestamps as necessary, and all current callers of rtpenc_chain
use ff_write_chained, making this timebase copy unnecessary.
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>
(cherry picked from commit 397ffde1)

libavformat/rtpenc_chain.c

@@ -70,8 +70,6 @@ AVFormatContext *ff_rtp_chain_mux_open(AVFormatContext *s, AVStream *st,
         return NULL;
     }
 
-    /* Copy the RTP AVStream timebase back to the original AVStream */
-    st->time_base = rtpctx->streams[0]->time_base;
     return rtpctx;
 }