Remove remaining usages of skvx::mad

This CL attempts to remove the remaining subset of skvx::mad usages.
https://skia-review.googlesource.com/c/skia/+/304853 removes all usages
of skvx::mad but causes small differences in rendering, so it is not
suitable for landing.

https://skia-review.googlesource.com/c/skia/+/306702/ removes all
non-nested usages of skvx::mad

Change-Id: Iab5d4cfd0feb856c38b3ebbfe3bf3ed5aad20fe6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306722
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Elliot Evans <elliotevans@google.com>
7 files changed