Drop tidbit about tor-ops@ from man page

Sebastian made the good point that we mention tor-ops@ in the man page. We should stop. The man page would do just as well without this sentence...

[[AuthoritativeDirectory]] **AuthoritativeDirectory** **0**|**1**::
    When this option is set to 1, Tor operates as an authoritative directory
    server. Instead of caching the directory, it generates its own list of
    good servers, signs it, and sends that to the clients. Unless the clients
    already have you listed as a trusted directory, you probably do not want
    to set this option. Please coordinate with the other admins at
    tor-ops@torproject.org if you think you should be a directory.