Remove SkShader::asAGradient

This was only available in Android Framework and is no longer used
there.

Bug: skia:8941
Change-Id: I73dec26b789991c4b8c1206b19746f7715e3e060
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/596316
Auto-Submit: Brian Salomon <bsalomon@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
3 files changed