Revert "Add Alpha Channel Support For WebRTC Unity Plugin"

This reverts commit 7ed2af5b461387191de2456cba906dd5d25766b6.

Reason for revert: breaking buildbot

Original change's description:
> Add Alpha Channel Support For WebRTC Unity Plugin
> 
> This CL make webrtc unity plugin compatible with alpha channel support.
> 
> Bug: webrtc:8645
> Change-Id: I3250aede47b31c4685e57d11fb2b2e86b824f9c4
> Reviewed-on: https://webrtc-review.googlesource.com/32325
> Commit-Queue: Qiang Chen <qiangchen@chromium.org>
> Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
> Reviewed-by: George Zhou <gyzhou@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#21394}

TBR=magjed@webrtc.org,gyzhou@chromium.org,qiangchen@chromium.org

Change-Id: I6994d7e87170f97216886a747548a988ca71b7d0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8645
Reviewed-on: https://webrtc-review.googlesource.com/35420
Reviewed-by: Lu Liu <lliuu@webrtc.org>
Commit-Queue: Lu Liu <lliuu@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21396}
diff --git a/examples/unityplugin/simple_peer_connection.cc b/examples/unityplugin/simple_peer_connection.cc
index bffd5f6..2ea8227 100644
--- a/examples/unityplugin/simple_peer_connection.cc
+++ b/examples/unityplugin/simple_peer_connection.cc
@@ -16,16 +16,8 @@
 #include "api/audio_codecs/builtin_audio_encoder_factory.h"
 #include "api/test/fakeconstraints.h"
 #include "api/videosourceproxy.h"
-#include "media/engine/stereocodecfactory.h"
 #include "media/engine/webrtcvideocapturerfactory.h"
-#include "media/engine/webrtcvideodecoderfactory.h"
-#include "media/engine/webrtcvideoencoderfactory.h"
-#include "media/engine/internaldecoderfactory.h"
-#include "media/engine/internalencoderfactory.h"
-#include "modules/audio_device/include/audio_device.h"
-#include "modules/audio_processing/include/audio_processing.h"
 #include "modules/video_capture/video_capture_factory.h"
-#include "rtc_base/ptr_util.h"
 
 #if defined(WEBRTC_ANDROID)
 #include "examples/unityplugin/classreferenceholder.h"
@@ -102,14 +94,7 @@
     g_peer_connection_factory = webrtc::CreatePeerConnectionFactory(
         g_worker_thread.get(), g_worker_thread.get(), g_signaling_thread.get(),
         nullptr, webrtc::CreateBuiltinAudioEncoderFactory(),
-        webrtc::CreateBuiltinAudioDecoderFactory(),
-        std::unique_ptr<webrtc::VideoEncoderFactory>(
-            new webrtc::StereoEncoderFactory(
-                rtc::MakeUnique<webrtc::InternalEncoderFactory>())),
-        std::unique_ptr<webrtc::VideoDecoderFactory>(
-            new webrtc::StereoDecoderFactory(
-                rtc::MakeUnique<webrtc::InternalDecoderFactory>())),
-        nullptr, nullptr);
+        webrtc::CreateBuiltinAudioDecoderFactory(), nullptr, nullptr);
   }
   if (!g_peer_connection_factory.get()) {
     DeletePeerConnection();