[session] make security_enabled API private
The doc already says "internal API". The old entry point is now officially
deprecated and the context manager have been made private.
# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s schema"""