Stop avoiding calling systemctl for tgtd on Fedora

The bug that lead to this workaround was fixed and an update is
available for Fedora:
  https://bugzilla.redhat.com/show_bug.cgi?id=797913

Keeping this workaround would be annoying as --skip-redirect doesn't
exist on all rpm-based distributions, and we'd have to remember using it
everywhere we interact with the tgtd service.

Change-Id: I22a5d4fe154ea04bd35d89db6d63734b5bd405aa

stack.sh

@@ -1735,8 +1735,7 @@ elif is_service_enabled n-vol; then
         sudo stop tgt || true
         sudo start tgt
     else
-        # bypass redirection to systemctl during restart
-        sudo /sbin/service --skip-redirect tgtd restart
+        restart_service tgtd
     fi
 fi