Revert "Change some platform libraries to use `part of URI`."

sdk/lib/io/platform.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.
 
-part of "dart:io";
+part of dart.io;
 
 /**
  * Information about the environment in which the current program is running.
  *
  * Platform provides information such as the operating system,
  * the hostname of the computer, the value of environment variables,
  * the path to the running program,
  * and so on.
  *
  * ## Get the URI to the current Dart script
@@ skipping 205 matching lines @@
   /**
    * The version of the current Dart runtime.
    *
    * The value is a [semantic versioning](http://semver.org)
    * string representing the version of the current Dart runtime,
    * possibly followed by whitespace and other version and
    * build details.
    */
   static String get version => _version;
 }