rm Sk3D.h -- long live SkMat4

Change-Id: Ib83ee6567b1a32f34364b7ac66a659eaeced3249
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272037
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
5 files changed