mod_ssl.xml: remove <override>Not applicable</override>

These tags generate a "Not applicable" section in
docs/manual/mod/overrides.html that doesn't make a lot of
sense, plus it breaks ./build.sh validate-xhtml.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1824951 13f79535-47bb-0310-9956-ffa450edef68