pullup #2558 to the 2.9 branch in time for RC2

git-svn-id: http://svn.openlayers.org/branches/openlayers/2.9@10185 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/XYZ.js

@@ -107,7 +107,6 @@ OpenLayers.Layer.XYZ = OpenLayers.Class(OpenLayers.Layer.Grid, {
         var y = Math.round((this.maxExtent.top - bounds.top) 
             / (res * this.tileSize.h));
         var z = this.map.getZoom();
-        var limit = Math.pow(2, z);
 
         var url = this.url;
         var s = '' + x + y + z;