ISTWCMS-4199: Remove unnecessary classes

Fixes issue introduced in 5f333f93.

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

@@ -125,11 +125,7 @@
 
         <li class="menu--item menu--item__parent">
 
-          {% set link_attributes_1 = {
-            'class': link_attributes.class|merge(['menu--link-parent']),
-            'href': parent.url
-          }  %}
-          <a{{ add_attributes(link_attributes_1) }}>
+          <a href="{{ parent.url }}" class="menu--link-parent">
 
             <span class="link-text">
               {% if parent.title %}