check shelf.editable instead of custom filter

bookwyrm/templates/book/book.html

@@ -161,12 +161,12 @@
                 {% for shelf in user_shelfbooks %}
                     <li class="box">
                         {% blocktrans with path=shelf.shelf.local_path shelf_name=shelf.shelf.name %}<a href="{{ path }}">{{ shelf_name }}</a>{% endblocktrans %}
-                        {% if shelf.shelf.identifier|is_shelf_type:"readthrough" %}
-                            {% include 'snippets/shelve_button/shelve_button.html' %}
-                        {% else %}
+                        {% if shelf.shelf.editable %}
                         <div class="mb-3">
                             {% include 'snippets/shelf_selector.html' with current=shelf.shelf class="is-small" %}
                         </div>
+                        {% else %}
+                        {% include 'snippets/shelve_button/shelve_button.html' %}
                         {% endif %}
                     </li>
                 {% endfor %}

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 %}

bookwyrm/templatetags/bookwyrm_tags.py

@@ -41,17 +41,6 @@ def get_book_description(book):
     return book.description or book.parent_work.description
 
 
-@register.filter(name="is_shelf_type")
-def is_shelf_type(current_shelf, shelf_type):
-    """is this shelf a readthrough shelf?"""
-    readthrough = current_shelf in ["to-read", "reading", "read"]
-    if shelf_type == "readthrough" and bool(readthrough):
-        return True
-    if shelf_type == "custom" and not readthrough:
-        return True
-    return False
-
-
 @register.filter(name="next_shelf")
 def get_next_shelf(current_shelf):
     """shelf you'd use to update reading progress"""