override index: remove invalid <override>s from directives

Remove the bogus "none" and "n/a" type <override>s from the
documentation. If a directive can't be put in .htaccess, it shouldn't
have an <override> element.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1793933 13f79535-47bb-0310-9956-ffa450edef68