Remove Expect from core library.

tests/standalone/io/directory_invalid_arguments_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";
 import "dart:io";
 
 class DirectoryInvalidArgumentsTest {
   static void testFailingList(Directory d, var recursive) {
     int errors = 0;
     var lister = d.list(recursive: recursive);
     lister.onError = (error) {
       errors += 1;
     };
     lister.onDone = (completed) {
@@ skipping 33 matching lines @@
   }
 
   static void testMain() {
     testInvalidArguments();
   }
 }
 
 main() {
   DirectoryInvalidArgumentsTest.testMain();
 }