ISTWCMS-4223: Remove unnecessary classes

Fixes issue introduced in e06027a6.

Original issue prevented duplicate class attributes by combining all the
classes. But the extra class attributes had been ignored by browsers.
This returns it to just the classes present previously.

source/_patterns/04-components/menu/menu.twig

@@ -123,10 +123,7 @@
 
         {% set menu_parent_hide = true %}
 
-        {% set additional_item_attributes_1 = {
-          'class': additional_item_attributes.class|merge(['menu--item', 'menu--item__parent'])
-        }  %}
-        <li{{ add_attributes(additional_item_attributes_1) }}>
+        <li class="menu--item menu--item__parent">
 
           {% set link_attributes_1 = {
             'class': link_attributes.class|merge(['menu--link-parent']),