Revert "Add sharedfrontend package"

pkg/sharedfrontend/lib/elements.dart

-// Copyright (c) 2015, 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.
-
-/// Shared element model between the dart analyzer and dart2js.
-
-library elements;
-
-/// The interface `Element` defines the behavior common to all of the elements
-/// in the element model. Generally speaking, the element model is a semantic
-/// model of the program that represents things that are declared with a name
-/// and hence can be referenced elsewhere in the code.
-abstract class Element {
-  // TODO(johnniwinther): Semantic difference. Setter names from the analyzer
-  // contain '=' but doesn't in dart2js.
-  // TODO(johnniwinther,paulberry,brianwilkerson): What about privacy? Maybe
-  // name should be the `Name` class in
-  // 'package:compiler/src/elements/names.dart'.
-  /// The name of this element, or `null` if this element does not have a name.
-  String get name;
-
-  /// The library that contains this element. This will be the element itself if
-  /// it is a library element.
-  LibraryElement get library;
-}
-
-/// The interface `LibraryElement` defines the behavior of elements representing
-/// a library.
-abstract class LibraryElement extends Element {
-
-}
-
-/// The interface `ClassElement` defines the behavior of elements that represent
-/// a class.
-abstract class ClassElement extends Element {
-
-}