Remove unneeded RegionOp parameter from GrSWMaskHelper

Callers were only ever passing kRelease_Op, so just remove the parameter.

Prechange inspired by
https://skia-review.googlesource.com/c/skia/+/655436


Change-Id: Ibe4460a34b35802cece01d9b17b7542c8b9378df
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/655820
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
4 files changed