Simplify SkRasterClip now that it's only intersect/diff

Bug: skia:10205
Change-Id: Id29a63783bd38e5977e94bf8e8d7fbb4fe16cb51
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/442279
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
7 files changed