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/unity_plugin_apis.h b/examples/unityplugin/unity_plugin_apis.h
index b32f9e2..814b967 100644
--- a/examples/unityplugin/unity_plugin_apis.h
+++ b/examples/unityplugin/unity_plugin_apis.h
@@ -19,11 +19,9 @@
 typedef void (*I420FRAMEREADY_CALLBACK)(const uint8_t* data_y,
                                         const uint8_t* data_u,
                                         const uint8_t* data_v,
-                                        const uint8_t* data_a,
                                         int stride_y,
                                         int stride_u,
                                         int stride_v,
-                                        int stride_a,
                                         uint32_t width,
                                         uint32_t height);
 typedef void (*LOCALDATACHANNELREADY_CALLBACK)();
@@ -49,8 +47,7 @@
 WEBRTC_PLUGIN_API int CreatePeerConnection(const char** turn_urls,
                                            const int no_of_urls,
                                            const char* username,
-                                           const char* credential,
-                                           bool mandatory_receive_video);
+                                           const char* credential);
 // Close a peerconnection.
 WEBRTC_PLUGIN_API bool ClosePeerConnection(int peer_connection_id);
 // Add a audio stream. If audio_only is true, the stream only has an audio