Remove test override of SkCanvas::getGrContext

This method is no longer called by anyone, and it's removed
from Skia in https://review.skia.org/317281. This unblocks that.

Change-Id: I84657335f992cd23799a0718dc3734b45abce93a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2413532
Auto-Submit: Adlai Holler <adlai@google.com>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807582}

cc/test/test_skcanvas.h

@@ -46,7 +46,6 @@ class MockCanvas : public SkNoDrawCanvas {
   void onDrawRect(const SkRect& rect, const SkPaint& paint) override {
     OnDrawRectWithColor(paint.getColor());
   }
-  GrContext* getGrContext() override { return context_.get(); }
   GrRecordingContext* recordingContext() override { return context_.get(); }
 
   MOCK_METHOD1(OnDrawPaintWithColor, void(SkColor));