*) remove some obsolete/unused defines from httpd.h.

*) remove DEFAULT_XFERLOG from main.c; it is never set/used
*) move ap_get_max_daemons() to ap_mpm.h
*) move DEFAULT_LISTENBACKLOG to mpm_common.h


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88103 13f79535-47bb-0310-9956-ffa450edef68