Revert "Fix obsolete parameter in Systemd script"

Revert "Fix obsolete parameter in Systemd script"

This reverts commit 592fb22c7fe4d291e630a2b6126312d088ce60d7.

We have the problem that Systemd doesn't expand shell variables
into our environment.

During the upgrade cycle this would maybe render a wrong PID file
location, thus resulting in wrong 'safe-reload' behaviour.

This is only for a clean upgrade path from 2.8.x to 2.9.0,
the proper fix is to ensure that the sysconfig file is empty
and keep our own defaults, or modified from the user.

refs #6434