Remove a usage of GrPixelConfig in SkGpuBlurUtils::GaussianBlur (take 2)

Bug: skia:6718
Change-Id: I6a0be1cab5543c3d76a041fcdc9ae9be4a3b179b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242822
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
21 files changed