I think they might be commenting on the fact that you've got this listed under the base game (which is basically just the game launcher without any episodes attached; Not actually sure why it's available in the giveaway list to begin with, especially since staff stated over four years ago that it was up in error and was planned to be removed), which is going to cause problems for entry (see comments below).

Basically, since it's a game launcher app that any part of the game uses, even just the free episode/demo is going to flag entrants as already owning the game, since all the site is checking against with this listing is base game ownership. Again, this listing should have been removed years ago due to how HITMAN games are structured, and was only available on SG to begin with due to the site's autosyncing not being able to tell that the base game wasn't "a real game".

If you tab through the "Select a Game" results a few pages when creating the giveaway and searching for HITMAN™ 2, you'll find HITMAN™ 2 - Standard Edition and HITMAN™ 2 - Gold Edition. You can also just search for those directly to pull them up immediately.

There shouldn't be any real consequences for you for just leaving the giveaway running as-is (though if you want to add some assurance for avoiding future problems, might be good to have the winner comment what version they received, which'll let you easily get the listing changed if needed).

On the other hand, since entrants can no longer reobtain the free episode and complimentary licenses can't be reactivated once removed from account (at least historically, not sure how Steam handles that at present), there's going to be some entrants that might be restricted from entry if you don't choose to remake the current listing as Standard or Gold edition.

Bright side? You don't have to confirm the winner's DLC ownership with the current listing (for example, if there's just one episode short of having the Standard Edition to begin with), so leaving things as-is would at least make it easier on you (and again, you can always just have staff change the listing after-the-fact with a Change Giveaway Game ticket, so long as the winner confirms content).

Add another complimentary license to your account, then delete it. See if you can restore it. If you can, you can just remove the Hitman Starter license, sync steam, enter the giveaway, then immediately un-remove the license.

That's all just to check if it's now possible to delete complimentary licenses without doing so permanently (you could always just google and try and get an answer that way), but I don't believe they've actually ever changed how that works (ie, I think it still deletes complimentary licenses permanently if you attempt to remove them).

Thus, in theory, one way or another, you'd have to permanently remove the starter license from your account to be able to enter giveaways for the game (or, at least, any for giveaways that use this particular listing).

If you're not playing the demo anymore anyway, it should be fine to just locate and back up any save files and just delete the game, you theoretically wouldn't lose any thing that way other than your ability to play the demo in the future.

Cool :)