mod_proxy: don't add the default port to the name of proxy workers. PR 57259.

ap_proxy_port_of_scheme() knows more default ports than apr_unparse_uri().


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1644503 13f79535-47bb-0310-9956-ffa450edef68