dot/gnus-local.el.distorted: Fix Gnus configuration after upgrade.

I'm dropping compatibility with old Gnuses.

  * Use `starttls' where possible for communicating with IMAP servers.
    Alas, that doesn't include Gmail.

  * Remove the attempt to use separate authentication files for
    different accounts.  Everything is now in `~/.gnus.authinfo', and
    IMAP credentials are keyed by server label, not address, for some
    reason.

  * Note that chiark doesn't have a proper certificate.  For some
    reason, `starttls-extra-arguments' in IMAP server stanze is a list,
    while in SMTP server stanze, it's a string.