Remove reference to scheduler in animation.

packages/flutter/lib/src/animation/scheduler.dart

@@ -1,5 +0,0 @@
-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-export '../scheduler/scheduler.dart';

packages/flutter/lib/src/animation/ticker.dart

@@ -4,7 +4,7 @@
 
 import 'dart:async';
 
-import 'scheduler.dart';
+import 'package:flutter/scheduler.dart';
 
 typedef TickerCallback(Duration elapsed);