Remove Expect from core library.

tests/standalone/io/directory_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.
 //
 // Directory listing test.
 
+import "package:expect/expect.dart";
 import "dart:io";
 import "dart:isolate";
 
 class DirectoryTest {
   static void testListing() {
     bool listedDir = false;
     bool listedFile = false;
 
     Directory directory = new Directory("").createTempSync();
     Directory subDirectory = new Directory("${directory.path}/subdir");
@@ skipping 594 matching lines @@
   testCreateTempErrorSync();
   testCreateTempError();
   testCreateExistingSync();
   testCreateExisting();
   testCreateDirExistingFileSync();
   testCreateDirExistingFile();
   testCreateRecursive();
   testCreateRecursiveSync();
   testRename();
 }