Delete compatibility alias webrtc::kI420

Bug: webrtc:7385, webrtc:10198
Change-Id: Ib18b6fc45f1bac7f4145d4fca384978a85b6c85e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/130481
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27461}

common_video/libyuv/include/webrtc_libyuv.h

@@ -29,10 +29,6 @@ namespace webrtc {
 // This is the max PSNR value our algorithms can return.
 const double kPerfectPSNR = 48.0f;
 
-// TODO(nisse): Some downstream apps call CalcBufferSize with
-// ::webrtc::kI420 as the first argument. Delete after they are updated.
-const VideoType kI420 = VideoType::kI420;
-
 // Calculate the required buffer size.
 // Input:
 //   - type         :The type of the designated video frame.