Revert my previous doc commit about upstream DNS resolution caching in...

Revert my previous doc commit about upstream DNS resolution caching in mod-proxy, there is still confusion in the users@ mailing list about what is the real behavior.  



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1746084 13f79535-47bb-0310-9956-ffa450edef68