check shelf.editable instead of custom filter

bookwyrm/templates/snippets/shelf_selector.html

@@ -9,7 +9,7 @@
 
 {% block dropdown-list %}
 {% for shelf in user_shelves %}
-{% if shelf.identifier|is_shelf_type:"custom" %}
+{% if shelf.editable %}
 <li role="menuitem" class="dropdown-item p-0">
     <form name="shelve" action="/shelve/" method="post">
         {% csrf_token %}