Revert of Remove unnecessary interface TelephoneEventHandler (patchset #3 id:40001 of https://codereview.webrtc.org/2357583002/ )

Reason for revert:
breaks downstream code

Original issue's description:
> Remove unnecessary interface TelephoneEventHandler.
>
> BUG=webrtc:2795
>
> Committed: https://crrev.com/2beb42983ca24e1326a9a7f2c06b3ad740eea2c3
> Cr-Commit-Position: refs/heads/master@{#14346}

TBR=henrik.lundin@webrtc.org,solenberg@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:2795

Review-Url: https://codereview.webrtc.org/2362673002
Cr-Commit-Position: refs/heads/master@{#14348}

webrtc/modules/rtp_rtcp/source/rtp_receiver_impl.h

@@ -57,6 +57,8 @@ class RtpReceiverImpl : public RtpReceiver {
 
   int32_t Energy(uint8_t array_of_energy[kRtpCsrcSize]) const override;
 
+  TelephoneEventHandler* GetTelephoneEventHandler() override;
+
  private:
   bool HaveReceivedFrame() const;