ITS#4338 delete extraneous slapd_close() calls. Descriptors that were in

ITS#4338 delete extraneous slapd_close() calls. Descriptors that were in
the event set must be removed using slapd_remove() and the whole sequence
must be protected with the slap_daemon.sd_mutex to close them properly.
Otherwise it will wind up closing valid, freshly opened sockets, or closing
dead sockets twice, etc. It's unnecessary to do any close management here
since connection.c already does the correct teardown sequence.