mention RewriteLog/RewriteLogLevel going away in 2.4 upgrading doc.

Submitted by: Sean Timmins
Committed by: covener



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1485752 13f79535-47bb-0310-9956-ffa450edef68