remove legacy pathref validation

Chrome added a public method to validate SkPathRef,
but always called it when validating SkPath. We did too.

Remove the SkPathRef entry point, validate SkPathRef
when validating SkPath, and remove Skia's callers.
(Chrome has already been fixed.)

TBR=reed@google.com
R=fmalita@chromium.org

Bug:913930
Change-Id: I0828b00b42cc1f031b4216ddeace50f80aa21e62
Reviewed-on: https://skia-review.googlesource.com/c/177065
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
3 files changed