remove experimental from some APIs (that are no longer experiments)

Change-Id: I614dc116307cbeefb26768e2fff423bb50603eaf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209168
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
3 files changed