call remove_ammo before removing the cut up item.

Fixes #7129

It also handles the gun mods that are attached to the gun (removes them from the item and adds them to the inventory). The function `remove_ammo` is already used by the crafting code to remove ammo from guns that are used in recipes.

It also prevents one from loosing the knife that is in a boot or the arrows that are in quiver, and all the other new container item, when cutting them up.