[connection] remove the `mode` attribute
It is now unused.
While removing mode, we also drop some sqlserver-specific reconnection logic snippets.
These had several downsides:
* untested
* partial coverage
* done at the wrong level
Related to #2919309.
# -*- 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 specific hooks and operations"""