Issue #29012: Remove another outdated information

Patch by Jim Fasarakis-Hilliard.

Doc/reference/datamodel.rst

@@ -765,9 +765,9 @@ Custom classes
    Special attributes: :attr:`~definition.__name__` is the class name; :attr:`__module__` is
    the module name in which the class was defined; :attr:`~object.__dict__` is the
    dictionary containing the class's namespace; :attr:`~class.__bases__` is a
-   tuple (possibly a singleton) containing the base classes, in the
-   order of their occurrence in the base class list; :attr:`__doc__` is the
-   class's documentation string, or ``None`` if undefined.
+   tuple containing the base classes, in the order of their occurrence in the
+   base class list; :attr:`__doc__` is the class's documentation string, or
+   ``None`` if undefined.
 
 Class instances
    .. index::