message: Removes rtp_transport checks in AudioSendStream
  There's already a DCHECK at construction time ensuring that it's set.
  Cr-Commit-Position: refs/heads/master@{#29393}
diff: @@ -195,21 +195,16 @@ AudioSendStream::AudioSendStream(
  ConfigureStream(config, true);
  pacer_thread_checker_.Detach();
  - if (rtp_transport_) {
  - // Signal congestion controller this object is ready for OnPacket*
  - // callbacks.
  + // Signal congestion controller this object is ready for OnPacket* callbacks.
  rtp_transport_->RegisterPacketFeedbackObserver(this);
  }
  -}
  AudioSendStream::~AudioSendStream() {
  RTC_DCHECK(worker_thread_checker_.IsCurrent());
  RTC_LOG(LS_INFO) << "~AudioSendStream: " << config_.rtp.ssrc;
  RTC_DCHECK(!sending_);
  - if (rtp_transport_) {
  rtp_transport_->DeRegisterPacketFeedbackObserver(this);
  channel_send_->ResetSenderCongestionControlObjects();
  - }
  // Blocking call to synchronize state with worker queue to ensure that there
  // are no pending tasks left that keeps references to audio.
  rtc::Event thread_sync_event;
  @@ -323,7 +318,6 @@ void AudioSendStream::ConfigureStream(
  // Probing in application limited region is only used in combination with
  // send side congestion control, wich depends on feedback packets which
  // requires transport sequence numbers to be enabled.
  - if (rtp_transport_) {
  // Optionally request ALR probing but do not override any existing
  // request from other streams.
  if (enable_audio_alr_probing_) {
  @@ -331,12 +325,9 @@ void AudioSendStream::ConfigureStream(
  }
  bandwidth_observer = rtp_transport_->GetBandwidthObserver();
  }
  - }
  - if (rtp_transport_) {
  channel_send_->RegisterSenderCongestionControlObjects(rtp_transport_,
  bandwidth_observer);
  }
  - }
  config_cs_.Enter();
  // MID RTP header extension.
  if ((first_time || new_ids.mid != old_ids.mid ||
  