Revert "Adding injectable audio decoder and encoder factory support to the RTCPeerConnection obj-c layer."

This reverts commit 96de428fd1f301c3ad1355183b45e44db5ef3f7f.

Reason for revert: Gives compile errors because the new ObjC++ headers are included in some targets that use ObjC.

Original change's description:
> Adding injectable audio decoder and encoder factory support to the RTCPeerConnection obj-c layer.
> 
> Bug: webrtc:8093
> Change-Id: I868ce5f75a72c6deb065dec60784289d045ae22a
> Reviewed-on: https://chromium-review.googlesource.com/608981
> Commit-Queue: Jeremy Newton-Smith <jeremyns@webrtc.org>
> Reviewed-by: Zeke Chin <tkchin@webrtc.org>
> Reviewed-by: Kári Tristan Helgason <kthelgason@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#19477}

TBR=kjellander@webrtc.org,tkchin@webrtc.org,kthelgason@webrtc.org,jeremyns@webrtc.org

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

Bug: webrtc:8093
Change-Id: I3ade9dd979c9f13990a2972b15b786b8e78e1cd4
Reviewed-on: https://chromium-review.googlesource.com/640810
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19573}
diff --git a/webrtc/sdk/BUILD.gn b/webrtc/sdk/BUILD.gn
index 2bbc785..cf31fe9 100644
--- a/webrtc/sdk/BUILD.gn
+++ b/webrtc/sdk/BUILD.gn
@@ -310,15 +310,9 @@
 
     rtc_static_library("peerconnectionfactory_objc") {
       sources = [
-        "objc/Framework/Classes/PeerConnection/RTCBuiltinAudioDecoderFactory.mm",
-        "objc/Framework/Classes/PeerConnection/RTCBuiltinAudioEncoderFactory.mm",
         "objc/Framework/Classes/PeerConnection/RTCPeerConnectionFactory+Private.h",
         "objc/Framework/Classes/PeerConnection/RTCPeerConnectionFactory.mm",
         "objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm",
-        "objc/Framework/Headers/WebRTC/RTCAudioDecoderFactory.h",
-        "objc/Framework/Headers/WebRTC/RTCAudioEncoderFactory.h",
-        "objc/Framework/Headers/WebRTC/RTCBuiltinAudioDecoderFactory.h",
-        "objc/Framework/Headers/WebRTC/RTCBuiltinAudioEncoderFactory.h",
       ]
 
       public_configs = [ ":common_config_objc" ]
@@ -337,8 +331,6 @@
         ":videotoolbox_objc",
         ":videotracksource_objc",
         "../api:video_frame_api",
-        "../api/audio_codecs:builtin_audio_decoder_factory",
-        "../api/audio_codecs:builtin_audio_encoder_factory",
         "../api/video_codecs:video_codecs_api",
         "../media:rtc_audio_video",
         "../media:rtc_media_base",
@@ -577,16 +569,15 @@
       ios_framework_bundle("framework_objc") {
         info_plist = "objc/Framework/Info.plist"
         output_name = "WebRTC"
+
         common_objc_headers = [
-          "objc/Framework/Headers/WebRTC/RTCAVFoundationVideoSource.h",
-          "objc/Framework/Headers/WebRTC/RTCAudioDecoderFactory.h",
-          "objc/Framework/Headers/WebRTC/RTCAudioEncoderFactory.h",
           "objc/Framework/Headers/WebRTC/RTCAudioSession.h",
+          "objc/Framework/Headers/WebRTC/RTCVideoCodec.h",
+          "objc/Framework/Headers/WebRTC/RTCVideoCodecFactory.h",
           "objc/Framework/Headers/WebRTC/RTCAudioSessionConfiguration.h",
+          "objc/Framework/Headers/WebRTC/RTCAVFoundationVideoSource.h",
           "objc/Framework/Headers/WebRTC/RTCAudioSource.h",
           "objc/Framework/Headers/WebRTC/RTCAudioTrack.h",
-          "objc/Framework/Headers/WebRTC/RTCBuiltinAudioDecoderFactory.h",
-          "objc/Framework/Headers/WebRTC/RTCBuiltinAudioEncoderFactory.h",
           "objc/Framework/Headers/WebRTC/RTCCameraVideoCapturer.h",
           "objc/Framework/Headers/WebRTC/RTCCameraPreviewView.h",
           "objc/Framework/Headers/WebRTC/RTCConfiguration.h",
@@ -618,8 +609,6 @@
           "objc/Framework/Headers/WebRTC/RTCSessionDescription.h",
           "objc/Framework/Headers/WebRTC/RTCTracing.h",
           "objc/Framework/Headers/WebRTC/RTCVideoCapturer.h",
-          "objc/Framework/Headers/WebRTC/RTCVideoCodec.h",
-          "objc/Framework/Headers/WebRTC/RTCVideoCodecFactory.h",
           "objc/Framework/Headers/WebRTC/RTCVideoFrame.h",
           "objc/Framework/Headers/WebRTC/RTCVideoFrameBuffer.h",
           "objc/Framework/Headers/WebRTC/RTCVideoRenderer.h",