systemctl,pid1: do not warn about missing install info with "preset"

systemctl,pid1: do not warn about missing install info with "preset"

When "preset" was executed for a unit without install info, we'd warn similarly
as for "enable" and "disable". But "preset" is usually called for all units,
because the preset files are provided by the distribution, and the units are under
control of individual programs, and it's reasonable to call "preset" for all units
rather then try to do it only for the ones that can be installed.
We also don't warn about missing info for "preset-all". Thus it seems reasonable
to silently ignore units w/o install info when presetting.

(In addition, when more than one unit was specified, we'd issue the warning
only if none of them had install info. But this is probably something to fix
for enable/disable too.)