Remove i420_video_frame.h from common_video.gyp

i420_video_frame.h was removed in
https://webrtc-codereview.appspot.com/46819004/
but common_video.gyp was not updated with this change.

BUG=N/A
TBR=tfarina@chromium.org

Review URL: https://webrtc-codereview.appspot.com/51569004

Cr-Commit-Position: refs/heads/master@{#8974}
diff --git a/webrtc/common_video/common_video.gyp b/webrtc/common_video/common_video.gyp
index 68f85aa..53e074b 100644
--- a/webrtc/common_video/common_video.gyp
+++ b/webrtc/common_video/common_video.gyp
@@ -42,7 +42,6 @@
         'i420_buffer_pool.cc',
         'i420_video_frame.cc',
         'interface/i420_buffer_pool.h',
-        'interface/i420_video_frame.h',
         'interface/video_frame_buffer.h',
         'libyuv/include/scaler.h',
         'libyuv/include/webrtc_libyuv.h',