Remove usage of dart:utf from dart:io.

tests/standalone/io/string_transformer_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 "dart:async";
 import "dart:convert";
 import "dart:io";
 import "dart:isolate";
-import "dart:utf";
 
 import "package:expect/expect.dart";
 
+const UNICODE_REPLACEMENT_CHARACTER_CODEPOINT = 0xFFFD;
+
 void main() {
   testUtf8();
   testLatin1();
   testAscii();
   testReadLine1();
   testReadLine2();
   testErrorHandler();
   testLatin1EncoderError();
 }
 
@@ skipping 168 matching lines @@
     .transform(new StringEncoder(Encoding.ISO_8859_1));
   stream.listen(
     (s) {
       Expect.fail("data not expected");
     },
     onError: (error) {
       Expect.isTrue(error is FormatException);
     });
 
 }