Remove GrBlendFragmentProcessor::BlendBehavior::kDefault

Always explicitly pass one of the other behaviors.

Bug: skia:10457
Change-Id: I573161b3de0476a398d71fcaab71e2d68fa13d02
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/425457
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
14 files changed