Remove support for multiple coverage processors from GrPaint API.

Change-Id: I82276e38ea4a5524127176eb5a34066b6cb06d88
Bug: skia:10217
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/304799
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
15 files changed