mpm_event: follow up to r1818804 and r1818951.

Be more correct in comment about CONN_STATE_WRITE_COMPLETION.
We currently have/need no state to simply wait for readability on a socket,
so the previous comment was misleading. Write completion can't be used for
a simple "wait for read event and come back to process_connection hooks".



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1819027 13f79535-47bb-0310-9956-ffa450edef68