rm clone-with-slug

Clones are rare, cloning is broken.
It makes more sense to clone from an item's page.

inventory-app/templates/inventory_add_slug.html

@@ -14,9 +14,6 @@ It can be assigned to an existing item or a new item can be created.
 <div class="row">
   <a href="/m/inventory/assign-slug/{{ slug }}" class="waves-effect waves-light btn">Assign to existing item</a>
 </div>
-<div class="row">
-  <a href="/m/inventory/clone-with-slug/{{ slug }}" class="waves-effect waves-light btn">Clone existing item</a>
-</div>
 
 </div>
 {% endblock %}