Don't call udevadm control --exit in systemd mode

This partly reverts commit a43f97c.

(cherry picked from commit 765d840)

https://bugzilla.redhat.com/show_bug.cgi?id=1276983

Author: haraldh

modules.d/98systemd/dracut-pre-pivot.sh

@@ -36,6 +36,4 @@ while ! udevadm settle --timeout=0; do
     [ $cnt -gt 10 ] && break
 done
 
-udevadm control --exit
-
 exit 0