mod_proxy: we don't need ap_proxy_ssl_connection_cleanup() anymore with

ap_proxy_check_backend() used at connection reuse time, so remove its last call and deprecate it.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1750416 13f79535-47bb-0310-9956-ffa450edef68