authentic: ignore date attributes for now

authentic/export-users.py

@@ -40,6 +40,8 @@ def to_json(user):
     }
     for av in AttributeValue.objects.with_owner(user):
         # XXX: this should also export av.verified
+        if av.attribute.kind in ('date', 'birthdate'):
+            continue
         user_dict['attributes'][str(av.attribute.name)] = av.to_python()
 
     return user_dict