Remove GrBlendFragmentProcessor::BlendBehavior.

There is only one value for the enum.

Bug: skia:10457
Change-Id: I46edd905c3a65ab5b398964ccd4f978b9b9737f9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/425461
Reviewed-by: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
15 files changed