remove duplicated prop copying

lib/browser/api/menu.js

@@ -295,12 +295,6 @@ Menu.buildFromTemplate = function (template) {
       throw new TypeError('Invalid template for MenuItem')
     }
     menuItem = new MenuItem(item)
-    for (key in item) {
-      // Preserve extra fields specified by user
-      if (!menuItem.hasOwnProperty(key)) {
-        menuItem[key] = item[key]
-      }
-    }
     menu.append(menuItem)
   }
   return menu