Backport:

mod_proxy: Remove dead code from the public API, move single use code out
of the public API, remove redundant code from the public API.
mod_cache: Remove redundant code from the public API.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1209960 13f79535-47bb-0310-9956-ffa450edef68