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>

Author: reed-at-google

gn/utils.gni

@@ -29,7 +29,6 @@ skia_utils_public = [
 ]
 
 skia_utils_sources = [
-  "$_src/utils/Sk3D.cpp",
   "$_src/utils/SkAnimCodecPlayer.cpp",
   "$_src/utils/SkBase64.cpp",
   "$_src/utils/SkBitSet.h",

include/utils/Sk3D.h

@@ -128,7 +128,6 @@ if (skia_enable_skottie) {
 
         configs += [ "../..:skia_private" ]
         sources = [
-          "gm/3dgm.cpp",
           "gm/ExternalProperties.cpp",
           "gm/SkottieGM.cpp",
         ]