remove leader, perchild, and threadpool MPMs (other than non-English bits in...

remove leader, perchild, and threadpool MPMs (other than non-English bits in common parts of the manual)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@758613 13f79535-47bb-0310-9956-ffa450edef68