Remove a usage of GrPixelConfig in SkGpuBlurUtils::GaussianBlur

Bug: skia:6718
Change-Id: Ia8a96cf6907ffaafd989f1e5bb1443d1ef51b9e6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242142
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
18 files changed