rtpdec: Remove a useless todo comment

The question can be answered: No, we do not know the initial sequence
number from the SDP. In certain cases, it can be known from the
RTP-Info response header in RTSP though. (In that case, we use it as
timestamp origin, but not for rtp receiver statistics.)
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtpdec.c

@@ -482,7 +482,7 @@ RTPDemuxContext *ff_rtp_parse_open(AVFormatContext *s1, AVStream *st,
     s->ic                  = s1;
     s->st                  = st;
     s->queue_size          = queue_size;
-    rtp_init_statistics(&s->statistics, 0); // do we know the initial sequence from sdp?
+    rtp_init_statistics(&s->statistics, 0);
     if (!strcmp(ff_rtp_enc_name(payload_type), "MP2T")) {
         s->ts = ff_mpegts_parse_open(s->ic);
         if (s->ts == NULL) {