Revert "RtpTransceiverInterface: introduce SetOfferedRtpHeaderExtensions."

This reverts commit 71db9acc4019b8c9c13b14e6a022cbb3b4255b09.

Reason for revert: breaks downstream project.
Reason for force push: win bot broken.

Original change's description:
> RtpTransceiverInterface: introduce SetOfferedRtpHeaderExtensions.
>
> This change adds exposure of a new transceiver method for
> modifying the extensions offered in the next SDP negotiation,
> following spec details in https://w3c.github.io/webrtc-extensions/#rtcrtptransceiver-interface.
>
> Features:
> - The interface allows to control the negotiated direction as
>   per https://tools.ietf.org/html/rfc5285#page-7.
> - The interface allows to remove an extension from SDP
>   negotiation by modifying the direction to
>   RtpTransceiverDirection::kStopped.
>
> Note: support for signalling directionality of header extensions
> in the SDP isn't implemented yet.
>
> https://chromestatus.com/feature/5680189201711104.
> Intent to prototype: https://groups.google.com/a/chromium.org/g/blink-dev/c/65YdUi02yZk
>
> Bug: chromium:1051821
> Change-Id: Iaabc34446f038c46d93c442e90c2a77f77d542d4
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176408
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Commit-Queue: Markus Handell <handellm@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#31487}

TBR=hta@webrtc.org,handellm@webrtc.org

# Not skipping CQ checks because original CL landed > 1 day ago.

No-Try: true
Bug: chromium:1051821
Change-Id: I70e1a07225d7eeec7480fa5577d8ff647eba6902
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/177103
Commit-Queue: Markus Handell <handellm@webrtc.org>
Reviewed-by: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31516}

api/rtp_transceiver_interface.cc

@@ -41,10 +41,4 @@ RtpTransceiverInterface::HeaderExtensionsToOffer() const {
   return {};
 }
 
-webrtc::RTCError RtpTransceiverInterface::SetOfferedRtpHeaderExtensions(
-    rtc::ArrayView<const RtpHeaderExtensionCapability>
-        header_extensions_to_offer) {
-  return webrtc::RTCError(webrtc::RTCErrorType::UNSUPPORTED_OPERATION);
-}
-
 }  // namespace webrtc