Remove Expect from core library.

tests/compiler/dart2js/strip_comment_test.dart

 // Copyright (c) 2013, 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.
 
 library strip_comment_test;
 
+import "package:expect/expect.dart";
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart';
 
 testComment(String strippedText, String commentText) {
   Expect.stringEquals(strippedText, stripComment(commentText));
 }
 
 void main() {
   testComment('', '//');
   testComment('', '// ');
   testComment(' ', '//  ');
@@ skipping 53 matching lines @@
           * foo
           * bar
           * baz*/''');
   testComment('\nfoo\nbar\nbaz\n',
       '''/**
           * foo
           * bar
           * baz
           */''');
 }