Revert "Use a "decal" domain for filterMaskGPU"

This reverts commit a37ea9246e1e917eafb43ba3880220db26ceb5d9.

Reason for revert: Perf regressions

Original change's description:
> Use a "decal" domain for filterMaskGPU
> 
> In addition to requiring absClear, the old approach yielded
> asymmetrical blurs where the top and left edges got a "clamp" mode,
> and the right and bottom edges effectively got a "decal" mode.
> 
> Bug: skia:
> Change-Id: If72da4374eb2f0475acae59e269d44cb72c5ce95
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/240759
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>
> Commit-Queue: Chris Dalton <csmartdalton@google.com>

TBR=robertphillips@google.com,csmartdalton@google.com,michaelludwig@google.com

Change-Id: I653fd59401c06914cbe85bca77175e3fb182bc73
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242502
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
5 files changed