Move SkCubicSolver out of opts

This was only specialized to get fma, and only on Haswell. The code is
only used in skottie, and the net speedup to a cubic-map microbench was
very small (~20%). Overall, it hardly seems worth the trouble.

Change-Id: I82de38be05186747e8ccdeb2d6215a0c21bcf5fe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/664580
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
8 files changed