Move ownership of RTPSenderAudio to ChannelSend.

This change takes out responsibility for packetization from the
RtpRtcp class, and deletes the method RtpRtcp::SendOutgoingData.

Video packetization was similarly moved in cl
https://webrtc-review.googlesource.com/c/src/+/123187

Bug: webrtc:7135
Change-Id: I0953125a5ca22a2ce51761b83693e0bb8ea74cd8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/125721
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27000}

modules/rtp_rtcp/source/rtp_sender_audio.cc

@@ -47,7 +47,9 @@ const char* FrameTypeToString(FrameType frame_type) {
 }  // namespace
 
 RTPSenderAudio::RTPSenderAudio(Clock* clock, RTPSender* rtp_sender)
-    : clock_(clock), rtp_sender_(rtp_sender) {}
+    : clock_(clock), rtp_sender_(rtp_sender) {
+  RTC_DCHECK(clock_);
+}
 
 RTPSenderAudio::~RTPSenderAudio() {}