remove legacy 255-biased colormatrix

Bug: skia:4872
Bug: skia:9012

Change-Id: I7c1ac4e94405404fcb13079b5b578a5a26aad02e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/210628
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
3 files changed