Hi,
Go to condition table v/04 or v/03 - enter the table no.: XX - click on technical view box - there you will find KEY - this check box determine whether the fields will be a key field or not.
But why you want to remove the mandatory tick, it basically like a check which remind the user to maintain the value so that the same can be used to fetched the value while transaction.
If you want to remove the tick then why you are not creating a new key combination i.e. condition table v/03?
Thanks.
SS