If you want to have an AAV without its grenade launcher at Mission start, simply write this into the AAVs Init-Line
this removeWeapon "MK19"; this removeMagazine "48Rnd_40mm_MK19";
I do not know how many Magazines are in one AAV for its 40mm. RemoveMagazine will only remove one, so you´ll have to write it as many times as there are Magazines.