remove unused SkPoint3 from SkColor.h

Bug: skia:
Change-Id: Iba327a5604dc11525c4d8d0a535a7c417a1b8185
Reviewed-on: https://skia-review.googlesource.com/25961
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
7 files changed