Clean up in module_common_types.h by removing the unused struct RTPAudioHeader.

By removing it we can in turn (next CL) get rid of RTPTypeHeader, which is a
union that cause some problems.

Bug: none
Change-Id: I9246ecbfe2c8b7eda27497cccbc5f438958b64bf
Reviewed-on: https://webrtc-review.googlesource.com/83985
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23666}

modules/rtp_rtcp/source/rtp_receiver_impl.h

@@ -54,8 +54,6 @@ class RtpReceiverImpl : public RtpReceiver {
 
   int32_t CSRCs(uint32_t array_of_csrc[kRtpCsrcSize]) const override;
 
-  int32_t Energy(uint8_t array_of_energy[kRtpCsrcSize]) const override;
-
   TelephoneEventHandler* GetTelephoneEventHandler() override;
 
   std::vector<RtpSource> GetSources() const override;