Remove custom elements examples, they are no longer maintained

sky/framework/elements/sky-ink-splash.sky

 <!--
 // 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.
 -->
 <import src="sky-element.sky" />
 
 <sky-element>
 <template>
   <style>
@@ skipping 13 matching lines @@
       border-radius: 0;
       top: 0;
       left: 0;
       height: 0;
       width: 0;
     }
   </style>
   <div id="splash" />
 </template>
 <script>
-import "../animation/controller.dart";
 import "../animation/curves.dart";
-import "../animation/timer.dart";
+import "animation/controller.dart";
+import "animation/timer.dart";
 import "dart:math" as math;
 import "dart:sky";
 import "dart:async";
 
 const double _kSplashSize = 400.0;
 const double _kSplashDuration = 500.0;
 
 @Tagname('sky-ink-splash')
 class SkyInkSplash extends SkyElement implements AnimationDelegate {
   AnimationController _animation;
@@ skipping 42 matching lines @@
     _splash.style['width'] = '${p}px';
     _splash.style['height'] = '${p}px';
     _splash.style['border-radius'] = '${p}px';
     _splash.style['opacity'] = '${1.0 - (p / _kSplashSize)}';
   }
 }
 
 _init(script) => register(script, SkyInkSplash);
 </script>
 </sky-element>