Agility, can swing quiken be removed?

well that pretty much sums it up, can I remove the speed bonus from agility?

try looking in gameplay constants maybe

been there, done that, nope(lol)

Try putting the Hero's Agility gained per level to 0?

It is probably hardcoded. If you could figure out the attack speed bonus per agility you could counter it with the gloves of haste ability.