BUG/MEDIUM: kqueue: Don't bother closing the kqueue after fork.

kqueue fd's are not shared with children after fork(), so the children
don't have to close them, and it may in fact be dangerous, because we may
end up closing a totally unrelated fd.

[wt: to be backported to 1.8 where master-worker broke on this, and
 likely to older versions for completeness]
diff --git a/src/ev_kqueue.c b/src/ev_kqueue.c
index b61fe65..b42ee3d 100644
--- a/src/ev_kqueue.c
+++ b/src/ev_kqueue.c
@@ -216,8 +216,6 @@
  */
 REGPRM1 static int _do_fork(struct poller *p)
 {
-	if (kqueue_fd >= 0)
-		close(kqueue_fd);
 	kqueue_fd = kqueue();
 	if (kqueue_fd < 0)
 		return 0;