Remove Expect from core library.

tests/standalone/io/socket_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 NotAnInteger {
   operator==(other) => other == 1;
   operator<(other) => other > 1;
   operator+(other) => 1;
 }
 
 class NotAList {
   get length => 10;
@@ skipping 47 matching lines @@
   testReadList([1, 2, 3], 1, new NotAnInteger());
   testWriteList(null, 123, 123);
   testWriteList(new NotAList(), 1, 1);
   testWriteList([1, 2, 3], new NotAnInteger(), new NotAnInteger());
   testWriteList([1, 2, 3], 1, new NotAnInteger());
   testWriteList([1, 2, 3], new NotAnInteger(), 1);
   testServerSocketCreation(123, 123, 123);
   testServerSocketCreation("string", null, null);
   testServerSocketCreation("string", 123, null);
 }