Where's "Unsubscribe" on the Workshop page of America's Army in Steam?
Go to the page for the item you want to unsubscribe from, to see the Unsubscribe option.
Or go to the list of your items / your items from this game, and there should be a list of "Unsubscibe" options.
The list should be in Community -> Workshop:
Below the "Browse All Workshops" section, your profile picture should be beside a "Your Workshop Files" link. Click that and there's a list of the items you have.