remove unused dragElement.init option 'doubleclick'

Author: alexcjohnson

src/plots/cartesian/dragbox.js

@@ -130,7 +130,6 @@ module.exports = function dragBox(gd, plotinfo, x, y, w, h, ns, ew) {
         element: dragger,
         gd: gd,
         plotinfo: plotinfo,
-        doubleclick: doubleClick,
         prepFn: function(e, startX, startY) {
             var dragModeNow = gd._fullLayout.dragmode;