Answer:
Antifreeze is water soluble. You can use water to rinse the anti-freeze out of the carpeting provided you remove the carpeting from the car first. You don't want to put water on the carpet on the car while it is in the car because water will cause the floor to rust and holes in the floor are bad. The antifreeze, left in place, will not cause this problem. Note that wet carpet must be allowed to fully dry before being put back in place. This can take a few days.
If you are unable to remove the carpet from the car to rinse it, just wait a few months or so for the anti-freeze to dry on its own. It will stain, but you will still have a floor.