skia/BUILD.gn: remove SkLayer

BUG=

Review-Url: https://codereview.chromium.org/2660353002
diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index 178b694..3384227 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -229,7 +229,6 @@
     "//third_party/skia/src/utils/SkDumpCanvas.cpp",
     "//third_party/skia/src/utils/SkFrontBufferedStream.cpp",
     "//third_party/skia/src/utils/SkInterpolator.cpp",
-    "//third_party/skia/src/utils/SkLayer.cpp",
     "//third_party/skia/src/utils/SkMeshUtils.cpp",
     "//third_party/skia/src/utils/SkParsePath.cpp",
   ]