Documentation for mod_authn_alias is no longer needed since the only directive...

Documentation for mod_authn_alias is no longer needed since the only directive it documented has been merged in to mod_authn_core.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@373047 13f79535-47bb-0310-9956-ffa450edef68