Remove SkSurface::getContext

Change-Id: Ia683f717a5d8c43da5ff0a05219db86ca5bde2e8
Cq-Include-Trybots: luci.skia.skia.primary:Canary-Android,Canary-Chromium,Canary-Flutter,Canary-G3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317109
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Adlai Holler <adlai@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
5 files changed