Remove deprecated dart:utf library.

sdk/lib/_internal/libraries.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 libraries;
 
 /**
  * A bit flag used by [LibraryInfo] indicating that a library is used by dart2js
  */
 const int DART2JS_PLATFORM = 1;
@@ skipping 94 matching lines @@
       "typed_data/typed_data.dart",
       maturity: Maturity.STABLE,
       dart2jsPath: "typed_data/dart2js/typed_data_dart2js.dart"),
 
   "svg": const LibraryInfo(
       "svg/dartium/svg_dartium.dart",
       category: "Client",
       maturity: Maturity.WEB_STABLE,
       dart2jsPath: "svg/dart2js/svg_dart2js.dart"),
 
-  "utf": const LibraryInfo(
-      "utf/utf.dart",
-      maturity: Maturity.DEPRECATED),
-
   "web_audio": const LibraryInfo(
       "web_audio/dartium/web_audio_dartium.dart",
       category: "Client",
       maturity: Maturity.WEB_STABLE,
       dart2jsPath: "web_audio/dart2js/web_audio_dart2js.dart"),
 
   "web_gl": const LibraryInfo(
       "web_gl/dartium/web_gl_dartium.dart",
       category: "Client",
       maturity: Maturity.WEB_STABLE,
@@ skipping 158 matching lines @@
     "The library is stable. API backwards-compatibility is guaranteed.\n"
     "However implementation details might change.");
 
   static const Maturity LOCKED = const Maturity(5, "Locked",
     "This library will not change except when serious bugs are encountered.");
 
   static const Maturity UNSPECIFIED = const Maturity(-1, "Unspecified",
     "The maturity for this library has not been specified.");
 }