Remove Expect from core library.

tests/compiler/dart2js_extra/closure_capture2_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";
+
 closure0() {
   // f and g will both capture a variable named 'x'. If we use the original
   // name in the (shared) box then there will be troubles.
   var f;
   var g;
   {
     var x = 499;
     // TODO(floitsch): remove name from functions.
     f = fun() { return x; };
     x++;
@@ skipping 15 matching lines @@
   // TODO(floitsch): remove name from functions.
   var f = fun() { return $1; };
   $1++;
   Expect.equals(500, f());
 }
 
 main() {
   closure0();
   closure1();
 }