Remove Expect from core library.

tests/language/named_argument_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.
 
+import "package:expect/expect.dart";
+
 main() {
   var c1 = ({b, a}) => 'a: $a b: $b';
   var c2 = ({a, b}) => 'a: $a b: $b';
 
   Expect.equals ('a: 2 b: 1', c1(b: 1, a: 2));
   Expect.equals ('a: 1 b: 2', c1(a: 1, b: 2));
 
   Expect.equals ('a: 2 b: 1', c2(b: 1, a: 2));
   Expect.equals ('a: 1 b: 2', c2(a: 1, b: 2));
 }