I couldn't really make out what you exactly want, so I tried two possibilities :
if you want to delete the parachutes, just type somewhere :
deletevehicle vehicle _myunit
The guy will simply fall to the ground with no parachute.
if you want the guy to get rid of his chute, but the chute keeps falling to the ground by itself (that is, with no driver), then I don't think it's possible. :-\