Remove unused GrCubicEffect

Bug: skia:
Change-Id: I47e4b1e96905e27aed78cc317d0b7f263b8cf25a
Reviewed-on: https://skia-review.googlesource.com/c/166760
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
4 files changed