Remove Handler.MouseWheel mozilla workaround.

This workaround was created because of a mozilla bug [1] with
clientX, clientY on wheel events (DOMMouseScroll).

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=352179

lib/OpenLayers/Handler/MouseWheel.js

@@ -21,14 +21,6 @@ OpenLayers.Handler.MouseWheel = OpenLayers.Class(OpenLayers.Handler, {
      */
     wheelListener: null,
 
-    /** 
-     * Property: mousePosition
-     * {<OpenLayers.Pixel>} mousePosition is necessary because
-     * evt.clientX/Y is buggy in Moz on wheel events, so we cache and use the
-     * value from the last mousemove.
-     */
-    mousePosition: null,
-
     /**
      * Property: interval
      * {Integer} In order to increase server performance, an interval (in 
@@ -208,23 +200,7 @@ OpenLayers.Handler.MouseWheel = OpenLayers.Class(OpenLayers.Handler, {
         this.delta = 0;
         
         if (delta) {
-            // add the mouse position to the event because mozilla has 
-            // a bug with clientX and clientY (see 
-            // https://bugzilla.mozilla.org/show_bug.cgi?id=352179)
-            // getLonLatFromViewPortPx(e) returns wrong values
-            if (this.mousePosition) {
-                e.xy = this.mousePosition;
-            } 
-            if (!e.xy) {
-                // If the mouse hasn't moved over the map yet, then
-                // we don't have a mouse position (in FF), so we just
-                // act as if the mouse was at the center of the map.
-                // Note that we can tell we are in the map -- and 
-                // this.map is ensured to be true above.
-                e.xy = this.map.getPixelFromLonLat(
-                    this.map.getCenter()
-                );
-            }
+            e.xy = this.map.events.getMousePosition(e);
             if (delta < 0) {
                 this.callback("down", [e, this.cumulative ? delta : -1]);
             } else {
@@ -233,20 +209,6 @@ OpenLayers.Handler.MouseWheel = OpenLayers.Class(OpenLayers.Handler, {
         }
     },
     
-    /**
-     * Method: mousemove
-     * Update the stored mousePosition on every move.
-     * 
-     * Parameters:
-     * evt - {Event} The browser event
-     *
-     * Returns: 
-     * {Boolean} Allow event propagation
-     */
-    mousemove: function (evt) {
-        this.mousePosition = evt.xy;
-    },
-
     /**
      * Method: activate 
      */