Remove dart2js specific core.dart and coreimpl.dart files.

lib/compiler/implementation/lib/io.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.
 
 // This is a copy of the VM's dart:io library. This API is not usable
 // when running inside a web browser. Nevertheless, Leg provides a
 // mock version of the dart:io library so that it can statically
 // analyze programs that use dart:io.
 
 // TODO(ahe): Separate API from implementation details.
 
 /**
  * The IO library is used for Dart server applications,
  * which run on a stand-alone Dart VM from the command line.
  * *This library does not work in browser based applications.*
  *
  * This library allows you to work with files, directories,
  * sockets, processes, HTTP servers and clients, and more.
  */
 #library("dart:io");
+
 #import("dart:coreimpl");
 #import("dart:math");
 #import("dart:isolate");
 // TODO(ahe): Should Leg support this library?
 // #import("dart:nativewrappers");
 #import("dart:uri");
 #import("dart:crypto");
 #import("dart:utf");
+
 #source('../../../../runtime/bin/buffer_list.dart');
 #source('../../../../runtime/bin/common.dart');
 #source('../../../../runtime/bin/chunked_stream.dart');
 #source('../../../../runtime/bin/directory.dart');
 // Uses native keyword.
 // #source('../../../../runtime/bin/directory_impl.dart');
 // Uses native keyword.
 // #source('../../../../runtime/bin/eventhandler.dart');
 #source('../../../../runtime/bin/file.dart');
 // Uses native keyword.
@@ skipping 130 matching lines @@
   static void set _eventHandler(_EventHandler e) {
     throw new UnsupportedOperationException('_EventHandler._eventhandler = $e');
   }
 }
 
 const InputStream stdin = null;
 
 const OutputStream stdout = null;
 
 const OutputStream stderr = null;