Remove bad reference to non-existing SERVER_VERSION in mod_rewrite.html

Submitted by: Youichirou Koga <y-koga@jp.FreeBSD.ORG>
Reviewed by: Ralf S. Engelschall
PR: 2895


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@81954 13f79535-47bb-0310-9956-ffa450edef68