bpo-22039: [doc] clarify that there are no plans to disable deleting …

…an attribute via PyObject_SetAttr (pythonGH-30639)

(cherry picked from commit 3bf6315)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>

Doc/c-api/object.rst

@@ -81,8 +81,9 @@ Object Protocol
    return ``0`` on success.  This is the equivalent of the Python statement
    ``o.attr_name = v``.
 
-   If *v* is ``NULL``, the attribute is deleted, however this feature is
-   deprecated in favour of using :c:func:`PyObject_DelAttr`.
+   If *v* is ``NULL``, the attribute is deleted. This behaviour is deprecated
+   in favour of using :c:func:`PyObject_DelAttr`, but there are currently no
+   plans to remove it.
 
 
 .. c:function:: int PyObject_SetAttrString(PyObject *o, const char *attr_name, PyObject *v)