Miscellaneous blitter cleanup

- Remove the incredibly unlikely constant-in-y flag/optimization
- Remove manual ref-counting (!)

Change-Id: Iaba7813f0a6b9db07a2477ab60eec9b0f1b2806b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/683076
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
5 files changed