fail2ban: python packaging workaround for /etc/fail2ban installation (fixes #11534)

Removed path substitutions from setup.py because these should be handled
by the setuptools install prefix.

Except that the install prefix won't quite work until issue #4968 is
resolved.

In the meantime there are preInstall and postInstall scripts so that
this package continues to work with the nix python packaging
improvements.