remove unused yuv methods

Bug: skia:
Change-Id: Ie1e6c905d8989b49c2cf5c9e5fd1f383268f6480
Reviewed-on: https://skia-review.googlesource.com/14645
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
13 files changed