Prohibit gpu to raster in SkSpecialImage

Suspect this pathway isn't used, and we dont want to support it
in a future refactor requiring a GrDirectContext in getROPixels.

Bug: skia:104662
Change-Id: I9492fa7a6b85306d187c2eeab2463f305bd17dd0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/309720
Commit-Queue: Adlai Holler <adlai@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
1 file changed