Remove thread check from PacketRouter::SendFeedback.

R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1732923004 .

Cr-Commit-Position: refs/heads/master@{#11759}

webrtc/modules/pacing/packet_router.cc

@@ -123,7 +123,6 @@ uint16_t PacketRouter::AllocateSequenceNumber() {
 }
 
 bool PacketRouter::SendFeedback(rtcp::TransportFeedback* packet) {
-  RTC_DCHECK(pacer_thread_checker_.CalledOnValidThread());
   rtc::CritScope cs(&modules_crit_);
   if (::webrtc::SendFeedback(packet, &recv_rtp_modules_))
     return true;