In general, it's not very usuful to repeat the unit name as the description.
Especially when the word is a common name and if somebody doesn't understand
the meaning immediately, they are not going to gain anything from the
repeat either, e.g. "halt", "swap".
In the status-unit-format=combined output parentheses are used around
Description, so avoid using parenthesis in the Description itself.
Explicit systemctl calls remain in systemd-halt.service and the system
systemd-exit.service. To convert systemd-halt, we'd need to add
SuccessAction=halt-force. Halting doesn't make much sense, so let's just
leave that is. systemd-exit.service will be converted in the next commit.
