mod_slotmem_shm: follow up tp r1822509.

Do not bind attached slotmems to the global list, they should be detached when
pconf is cleaned up, but not destroyed/removed (doubly) with pglobal.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1823415 13f79535-47bb-0310-9956-ffa450edef68