On older systemd versions that don't support RestartMaxDelaySec /
RestartSteps, the installed unit file has those directives silently
dropped. systemd_unit_is_current() did a strict text comparison, so
the unit was perpetually flagged as outdated.
Fix: _strip_optional_systemd_directives() removes RestartMaxDelaySec
and RestartSteps from both the installed and expected text before
comparison. Units that differ only by these optional directives are
now correctly considered current.
