I know, but have you tried to start the game after removing those files? Good luck with that :)
Well yes, it makes calls to steam_api.dll library, which then does nothing. Therefore it won't work without the library, but the library itself will not really do anything, unless you actually own the game on Steam, have Steam itself installed and active on your system and put it into your Steam installed games folder, then make Steam detect it - that's a pretty damn contrived DRM scheme if I've ever seen one ;-) Including the file is more common than you'd think with games on GOG, and since it does nothing and is just added hassle to remove, there's absolutely no need to (unless you want indies waste their limited resources on something as pointless yet potentially time consuming). The only concern is how legal is distributing this file without Valve's persmission - then again, if Valve doesn't care, neither should we. It can lead to some weird bugs on some systems with Steam, but as long as you care about DRM-free, you probably don't even have Steam installed.