Remove (unused) YUV API from SkPixelRef

YUV conversion happens via SkImage now.

BUG=skia:

Change-Id: I6e1fa18effb72cbb00a173a346769b873e372c40
Reviewed-on: https://skia-review.googlesource.com/7034
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed