mpm_event: don't re-use scoreboard slots that are still in use

This causes inconsistent data in the scoreboard (due to async
connections) and makes it difficult to determine what is going on.
Therefore it is not a useful fix for the scoreboard-full issues (PR
53555).

The consent on the dev list is that we should allocate/use more
scoreboard entries instead.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1757031 13f79535-47bb-0310-9956-ffa450edef68