Delete legacy radial gradient impl

Raster pipeline FTW!

Change-Id: Ia2e600cf6c6e780f5a1519374c178197cf229776
Reviewed-on: https://skia-review.googlesource.com/29884
Commit-Queue: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
3 files changed