Remove unused SkRP load/store ops.

These ops were added early, when we thought we might use src.r as an
accumulator register. They aren't used today.

Change-Id: I24b966042748a938bb8bd1cad567c3580f4fe949
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/642656
Reviewed-by: Herb Derby <herb@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
6 files changed