Clean up examples directory

sky/examples/raw/circle.sky

 <sky>
 <style>
 div {
     height: 200px;
     background-color: lightblue;
 }
 </style>
 <div id="canvas" />
 <script>
 import 'dart:math' as math;
 import 'dart:sky';
 
 void main() {
   var element = document.getElementById('canvas');
   element.requestPaint((PaintingContext context) {
     Paint paint = new Paint();
     paint.setARGB(128, 0, 255, 0);
     double radius = math.min(context.width, context.height) / 2.0;
     context.drawCircle(context.width / 2.0, context.height / 2.0, radius, paint);
     context.commit();
   });
 }
 </script>
 </sky>