Remove Expect from core library.

tests/compiler/dart2js_extra/getters_setters_test.dart

 // Copyright (c) 2011, 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.
 
+import "package:expect/expect.dart";
+
 class GettersSettersTest {
 
   static int foo;
 
   static get bar {
     return foo;
   }
 
   static set bar(newValue) {
     foo = newValue;
@@ skipping 103 matching lines @@
   }
 
   void set x(int value) {
     y_ = value;
   }
 }
 
 main() {
   GettersSettersTest.testMain();
 }