Clean up WheelEvent

tools/dom/templates/html/dart2js/impl_ElementEvents.darttemplate

Index: tools/dom/templates/html/dart2js/impl_ElementEvents.darttemplate
diff --git a/tools/dom/templates/html/dart2js/impl_ElementEvents.darttemplate b/tools/dom/templates/html/dart2js/impl_ElementEvents.darttemplate
index 3e82f583024fa59b954970317079b999593d3849..3db967dbf8d614bd24bf783c615ea4dd3bdaa56f 100644
--- a/tools/dom/templates/html/dart2js/impl_ElementEvents.darttemplate
+++ b/tools/dom/templates/html/dart2js/impl_ElementEvents.darttemplate
@@ -8,16 +8,5 @@ part of $LIBRARYNAME;
 class $CLASSNAME extends $SUPER {
   $CLASSNAME(EventTarget _ptr) : super(_ptr);
 $!MEMBERS
-  EventListenerList get mouseWheel {
-    if (JS('bool', '#.onwheel !== undefined', _ptr)) {
-      // W3C spec, and should be IE9+, but IE has a bug exposing onwheel.
-      return this['wheel'];
-    } else if (JS('bool', '#.onmousewheel !== undefined', _ptr)) {
-      // Chrome & IE
-      return this['mousewheel'];
-    } else {
-      // Firefox
-      return this['DOMMouseScroll'];
-    }
-  }
+  EventListenerList get mouseWheel => this['wheel'];
 }