Fix the minedigger game.

Remove the Widgets framework's PointerEventListener definition now that
the Rendering layer has one. It was previously clashing in files that
imported both, which would result in it being hidden. Turns out
MineDigger is the only example that this affects.

packages/flutter/lib/src/widgets/framework.dart

@@ -8,15 +8,9 @@ import 'dart:sky' as sky;
 
 import 'package:sky/animation.dart';
 import 'package:sky/services.dart';
-import 'package:sky/src/rendering/box.dart';
-import 'package:sky/src/rendering/error.dart';
-import 'package:sky/src/rendering/hit_test.dart';
-import 'package:sky/src/rendering/object.dart';
-import 'package:sky/src/rendering/sky_binding.dart';
-import 'package:sky/src/rendering/view.dart';
+import 'package:sky/rendering.dart';
 
-export 'package:sky/src/rendering/box.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;
-export 'package:sky/src/rendering/object.dart' show Point, Offset, Size, Rect, Color, Paint, Path;
+export 'package:sky/rendering.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims, Point, Offset, Size, Rect, Color, Paint, Path;
 
 final bool _shouldLogRenderDuration = false; // see also 'enableProfilingLoop' argument to runApp()
 
@@ -685,8 +679,6 @@ abstract class Inherited extends TagNode {
 
 }
 
-typedef void PointerEventListener(sky.PointerEvent e);
-
 class Listener extends TagNode  {
   Listener({
     Key key,