Remove these files from BUILD.gn

They no longer exist but I forgot to remove them in my previous CL.

TBR=ianh@google.com

Review URL: https://codereview.chromium.org/1192603003.

sdk/BUILD.gn

@@ -54,24 +54,6 @@ dart_pkg("sdk") {
     "lib/framework/editing/editable_string.dart",
     "lib/framework/editing/editable_text.dart",
     "lib/framework/editing/keyboard.dart",
-    "lib/framework/elements/animation/controller.dart",
-    "lib/framework/elements/animation/timer.dart",
-    "lib/framework/elements/material-element.sky",
-    "lib/framework/elements/shadow.sky",
-    "lib/framework/elements/sky-box.sky",
-    "lib/framework/elements/sky-button.sky",
-    "lib/framework/elements/sky-checkbox.sky",
-    "lib/framework/elements/sky-drawer-header.sky",
-    "lib/framework/elements/sky-drawer.sky",
-    "lib/framework/elements/sky-element.sky",
-    "lib/framework/elements/sky-icon.sky",
-    "lib/framework/elements/sky-ink-splash.sky",
-    "lib/framework/elements/sky-input.sky",
-    "lib/framework/elements/sky-menu-divider.sky",
-    "lib/framework/elements/sky-menu-item.sky",
-    "lib/framework/elements/sky-radio.sky",
-    "lib/framework/elements/sky-scrollable.sky",
-    "lib/framework/elements/sky-toolbar.sky",
     "lib/framework/embedder.dart",
     "lib/framework/fn.dart",
     "lib/framework/layout.dart",