Remove CORE_PRIVATE.

This define serves no modern purpose, since every module in the wild, including 
our own define it, for no purpose.

If you have functions which you do not want in the 'public' API, put them
in a private header, that is not installed, just like mod_ssl does.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@645412 13f79535-47bb-0310-9956-ffa450edef68