message: remove legacy datachannel code
  Cr-Commit-Position: refs/heads/main@{#35634}
diff: @@ -297,7 +297,6 @@ bool PeerConnectionInterface::RTCConfiguration::operator==(
  bool disable_ipv6_on_wifi;
  int max_ipv6_networks;
  bool disable_link_local_networks;
  - bool enable_rtp_data_channel;
  absl::optional<int> screencast_min_bitrate;
  absl::optional<bool> combined_audio_video_bwe;
  absl::optional<bool> enable_dtls_srtp;
  