Remove unused (?) gradient context class

Bug: skia:
Change-Id: Id8a561e8d95fb0405cba2f2a5c3165667344579e
Reviewed-on: https://skia-review.googlesource.com/63860
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed