Remove Expect from core library.

tests/corelib/iterable_join_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";
+
 class IC {
   int count = 0;
   String toString() => "${count++}";
 }
 
 testJoin(String expect, Iterable iterable, [String separator]) {
   Expect.equals(expect, iterable.join(separator));
 }
 
 testCollections() {
@@ skipping 39 matching lines @@
     fixedArray[i] = i;
   }
   testArray(fixedArray);
   testArray(const [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
 }
 
 main() {
   testCollections();
   // TODO(lrn): test scalar lists.
 }