remove SkScalarFastInvert

Its implementation is just 1/x,
and looks like we never expect x == 0.

Change-Id: I405a3bd02b04d9ac0b13cea17573e32fc80ac0b2
Reviewed-on: https://skia-review.googlesource.com/c/168920
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed