Remove Expect from core library.

tests/standalone/io/fuzz_support.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.
 
 library fuzz_support;
 
+import 'package:expect/expect.dart';
 import 'dart:async';
 import 'dart:io';
 
 const typeMapping = const {
   'null': null,
   'int': 0,
   'bigint': 18446744073709551617,
   'String': 'a',
   'FileMode': FileMode.READ,
   'num': 0.50,
@@ skipping 27 matching lines @@
   try { f(); } catch (e) {}
 }
 
 // Perform async operation and transform the future for the operation
 // into a future that never fails by treating errors as normal
 // completion.
 Future doItAsync(void f()) {
   // Ignore value and errors.
   return new Future.delayed(0, f).catchError((_) {}).then((_) => true);
 }