Remove legacy gpu blur util code

TBR:michaelludwig@google.com

Bug: skia:10818
Change-Id: I1326aa017c0ed000efee1b9e0372a12976ba09eb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/324895
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Brian Salomon <bsalomon@google.com>
3 files changed