Remove GrBlendFragmentProcessor::Behavior::kSkBlendMode.

The only difference between this and kComposeOne is that it always
sets the src child's input color to opaque white. However, all call sites
pass a color FP that ignores its input. So in practice there is no
difference.

Bug: skia:10457
Change-Id: I816d421fcb7b48d81ba68f835571ef703aa8d73d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/425460
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
5 files changed