Removed obsolete references to add_to_query().

Support for it was removed in d3f00bd570.

django/db/models/query.py

@@ -796,13 +796,13 @@ class QuerySet:
         """
         Return a new QuerySet instance with filter_obj added to the filters.
 
-        filter_obj can be a Q object (or anything with an add_to_query()
-        method) or a dictionary of keyword lookup arguments.
+        filter_obj can be a Q object or a dictionary of keyword lookup
+        arguments.
 
         This exists to support framework features such as 'limit_choices_to',
         and usually it will be more natural to use other methods.
         """
-        if isinstance(filter_obj, Q) or hasattr(filter_obj, 'add_to_query'):
+        if isinstance(filter_obj, Q):
             clone = self._clone()
             clone.query.add_q(filter_obj)
             return clone

tests/or_lookups/models.py

@@ -5,8 +5,7 @@ To perform an OR lookup, or a lookup that combines ANDs and ORs, combine
 ``QuerySet`` objects using ``&`` and ``|`` operators.
 
 Alternatively, use positional arguments, and pass one or more expressions of
-clauses using the variable ``django.db.models.Q`` (or any object with an
-``add_to_query`` method).
+clauses using the variable ``django.db.models.Q``.
 """
 
 from django.db import models