Remove Expect from core library.

tests/standalone/package/packages/package1.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.
 
 library package1;
 
 import 'package2.dart' as p1;
 import 'package2.dart' as p2;
 import 'package:package2.dart' as p3;
 
 main() {
-  Expect.identical(p1.x, p2.x);
-  Expect.identical(p1.x, p3.x);
+  if (!identical(p1.x, p2.x)) {
+    throw new Error("Not identical");
+  }
+  if (!identical(p1.x, p3.x)) {
+    throw new Error("Not identical");
+  }
 }