Clean up GrPathUtils

Removes unused code, including utilities for dealing with KLM
functionals for the implicit cubic function. The implicit has proven
to not be a very good tool for rendering cubics.

Change-Id: I577b50a9eb296c52dc0101a20394480a4a008654
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/329440
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
5 files changed