Remove SkCanvas::getGrContext calls from benches

This will get us closer to deprecating getGrContext.

The benches have no SkSurface::getContext calls.

TBR=bsalomon@google.com
Change-Id: I6496a6324091a75d2829bd7ee20bdbe0dc3b6fe9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/300654
Reviewed-by: Adlai Holler <adlai@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
10 files changed