Remove obsolete manually defined _deltaX and _deltaY members.

tools/dom/templates/html/impl/impl_WheelEvent.darttemplate

 // Copyright (c) 2012, 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 $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
   factory WheelEvent(String type,
       {Window view, int deltaX: 0, int deltaY: 0,
@@ skipping 153 matching lines @@
 
   @DomName('WheelEvent.deltaMode')
   int get deltaMode {
     if (JS('bool', '!!(#.deltaMode)', this)) {
       return JS('int', '#.deltaMode', this);
     }
     // If not available then we're poly-filling and doing pixel scroll.
     return 0;
   }
 
-  num get _deltaY => JS('num', '#.deltaY', this);
-  num get _deltaX => JS('num', '#.deltaX', this);
   num get _wheelDelta => JS('num', '#.wheelDelta', this);
   num get _wheelDeltaX => JS('num', '#.wheelDeltaX', this);
   num get _detail => JS('num', '#.detail', this);
 
   bool get _hasInitMouseScrollEvent =>
       JS('bool', '!!(#.initMouseScrollEvent)', this);
 
   @JSName('initMouseScrollEvent')
   void _initMouseScrollEvent(
       String type,
@@ skipping 51 matching lines @@
    * [deltaMode].
    *
    * See also:
    *
    * * [WheelEvent.deltaY](http://dev.w3.org/2006/webapi/DOM-Level-3-Events/html/DOM3-Events.html#events-WheelEvent-deltaY) from the W3C.
    */
   @DomName('WheelEvent.deltaY')
   num get deltaY => _deltaY;
 $endif
 }