Revert "Add @deprecated and @override to core."

sdk/lib/core/metadata.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// part of dart_core;
-
-/**
- * An annotation used to mark a class, field, getter, setter, method, top-level
- * variable, or top-level function as one that should no longer be used. Tools
- * can use this annotation to provide a warning on references to the marked
- * element.
- */
-const deprecated = const Deprecated();
-
-class Deprecated {
-  final String message;
-  const Deprecated([this.message]);
-}
-
-/**
- * An annotation used to mark an instance member (method, field, getter or
- * setter) as overriding an inherited class member. Tools can use this
- * annotation to provide a warning if there is no overridden member.
- */
-const override = const _Override();
-
-class _Override {
-  const _Override();
-}