Replace SkDCubeRoot with std::cbrt

Unless there's a good reason for it, we should not need to
roll our own cube root algorithm.

Change-Id: I0c99fd5690c5a08c8922e1a0dbc0767445443dbb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/631421
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
4 files changed