mod_macro: fix usability of globally defined macros in .htaccess files.

PR 57525.

Reverts pre_config hook from r1656669 (happens too late for EXEC_ON_READ), and
ensures ap_macros is reset on restart with a pconf cleanup.

Proposed by: Jose Kahan <jose w3.org>
Reviewed by: ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1813643 13f79535-47bb-0310-9956-ffa450edef68