I don't see anywhere mentioning that it doesn't. I think it's obvious to make the experiment realistic one should aim for a close enough analogue of the Martian soil, and that would include perchlorates.
Commercially available martian soil simulants don’t contain perchlorates. Trying to obtain perchlorates is problematic, both from the health and law enforcement point of view.
you can remove perchlorates with dissimilatory perchlorate reducing bacteria, by rinsing the soil, by thermal decomposition in the soil, etc. there are many paths to perchlorate free soil since it is very reactive and water soluble
