Remove sky/engine/platform/clipboard

sky/engine/platform/BUILD.gn

Index: sky/engine/platform/BUILD.gn
diff --git a/sky/engine/platform/BUILD.gn b/sky/engine/platform/BUILD.gn
index 84b10f818bf2acabe5bb459d7501691121ff6b53..1b838bc821c6e20ad6c502fdd6c46344439f2c9c 100644
--- a/sky/engine/platform/BUILD.gn
+++ b/sky/engine/platform/BUILD.gn
@@ -165,11 +165,6 @@ source_set("platform") {
     "animation/TimingFunction.cpp",
     "animation/TimingFunction.h",
     "animation/UnitBezier.h",
-    "clipboard/ClipboardMimeTypes.cpp",
-    "clipboard/ClipboardMimeTypes.h",
-    "clipboard/ClipboardUtilities.cpp",
-    "clipboard/ClipboardUtilities.h",
-    "clipboard/ClipboardUtilitiesPosix.cpp",
     "exported/Platform.cpp",
     "exported/ServiceProvider.cpp",
     "exported/WebArrayBuffer.cpp",
@@ -659,7 +654,6 @@ test("platform_unittests") {
     "TestingPlatformSupport.h",
     "animation/TimingFunctionTest.cpp",
     "animation/UnitBezierTest.cpp",
-    "clipboard/ClipboardUtilitiesTest.cpp",
     "fonts/FontCacheTest.cpp",
     "fonts/FontDescriptionTest.cpp",
     "fonts/FontTest.cpp",