Remove deprecated parts of dart:async.

sdk/lib/async/schedule_microtask.dart

 // Copyright (c) 2013, 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.async;
 
 typedef void _AsyncCallback();
 
 bool _callbacksAreEnqueued = false;
 Queue<_AsyncCallback> _asyncCallbacks = new Queue<_AsyncCallback>();
@@ skipping 53 matching lines @@
   if (Zone.current == Zone.ROOT) {
     // No need to bind the callback. We know that the root's scheduleMicrotask
     // will be invoked in the root zone.
     Zone.current.scheduleMicrotask(callback);
     return;
   }
   Zone.current.scheduleMicrotask(
       Zone.current.bindCallback(callback, runGuarded: true));
 }
 
-/**
- * *DEPRECATED*. Use [scheduleMicrotask] instead.
- */
-@deprecated
-void runAsync(void callback()) {
-  scheduleMicrotask(callback);
-}
-
 class _AsyncRun {
   /** Schedule the given callback before any other event in the event-loop. */
   external static void _scheduleImmediate(void callback());
 }