Remove Expect from core library.

tests/compiler/dart2js/gvn_dynamic_field_get_test.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.
 // Test that dart2js gvns dynamic getters that don't have side
 // effects.
 
+import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST = r"""
 class A {
   var foo;
   bar(a) {
     return a.foo + a.foo;
   }
 }
@@ skipping 12 matching lines @@
   Iterator matches = regexp.allMatches(generated).iterator;
   checkNumberOfMatches(matches, 1);
   var cls = findElement(compiler, 'A');
   Expect.isNotNull(cls);
   SourceString name = buildSourceString('foo');
   var element = cls.lookupLocalMember(name);
   Expect.isNotNull(element);
   Selector selector = new Selector.getter(name, null);
   Expect.isFalse(compiler.world.hasAnyUserDefinedGetter(selector));
 }