Remove deprecated dart:utf library.

utils/tests/string_encoding/unicode_test.dart

 #!/usr/bin/env 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 unicode_tests;
 import 'dunit.dart';
-import '../../../sdk/lib/utf/utf.dart';
 
 void main() {
   TestSuite suite = new TestSuite();
   suite.registerTestClass(new UnicodeTests());
   suite.run();
 }
 
 class UnicodeTests extends TestClass {
   static const String testPhrase =
       "The quick brown fox jumps over the lazy dog.";
@@ skipping 19 matching lines @@
   }
 
   void testEmptyStringFromCharCodes() {
     Expect.stringEquals("", new String.fromCharCodes(<int>[]));
   }
 
   void testEmptyStringCharCodes() {
     Expect.listEquals([], "".codeUnits);
   }
 }