Fix elasticsearch search backend tests broken by #5208

wagtail/contrib/modeladmin/views.py

@@ -439,19 +439,9 @@ def get_ordering(self, request, queryset):
         # database backends.
         pk_name = self.opts.pk.name
 
-        if hasattr(self.model, 'get_filterable_search_fields'):
-            # The model is indexed, so let's be careful to only add
-            # indexed fields to ordering where possible
-            filterable_fields = self.model.get_filterable_search_fields()
-        else:
-            filterable_fields = None
-
         if not (set(ordering) & {'pk', '-pk', pk_name, '-' + pk_name}):
             # ordering isn't already being applied to pk
-            if filterable_fields is None or 'pk' in filterable_fields:
-                ordering.append('-pk')
-            else:
-                ordering.append('-' + pk_name)
+            ordering.append('-' + pk_name)
 
         return ordering
 

wagtail/tests/modeladmintest/models.py

@@ -33,7 +33,7 @@ class Book(models.Model, index.Indexed):
     search_fields = [
         index.SearchField('title'),
         index.FilterField('title'),
-        index.FilterField('pk'),
+        index.FilterField('id'),
     ]
 
     def __str__(self):