Remove unused SkRP op immediate_f.

This op would assign an immediate value to src.r. It's not used
anywhere, though, since we don't use src.rgba for computation in
SkRP. (Some RP tests used it as a filler op.)

Change-Id: I6061044c3dbf3134ee9fe0a3858e163a35549b46
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/642457
Reviewed-by: Herb Derby <herb@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Herb Derby <herb@google.com>
6 files changed