I don't believe that this was ever an option in the first place. I think you're getting confused with what the deboarding function actually does because as far as GSX is concerned, it always deboards everyone. If you have it set to estimate passenger numbers, it goes off the payload weight, so you never get asked for the numbers. If you don't have it set to estimate passenger numbers, if you've just started GSX, it'll ask you how many passengers you want to deboard. If you start boarding, it'll ask you how many passengers you want to board, and once you complete the flight, assuming GSX was running the entire time, it won't ask again since it already has the number you entered for the boarding. If, at some point, GSX was restarted after boarding for some reason, it would lose this number, and it would ask you how many passengers you want to deboard once you ask for deboarding.