This mirrors what was done in 564761fcae
for sysusers.d. If we allow separating resolved sysusers config
in a subpackage, we should do the same for the symlink that is
only useful when resolved is installed.
Related to #21317.
HAVE_SMACK_RUN_LABEL was dropped back in 348b44372f,
so one line in etc.conf was not rendered as expected ;(
Checking if names are defined is paying for itself!