There is no way to turn off a Wilding Village or Order of Asok. However, they will stop spawning new units after some number have been spawned (three Knights of Asok for the Order of Asok, I don't know how many for the Wilding Village). There must be some number of the units spawned from that resource present in your faction's unit list for that resource to stop spawning units.

You are well advised to disband Knights of Asok, since those cost an exceptionally high amount of money in wages. Until the wage cost of Knights of Asok is rebalanced, there is no reason to build the Order of Asok unless you're far enough ahead that 9 gold per turn per group of Knights doesn't completely trash your economy when you also have a halfway decent army. If you want to screw over an AI player, go to war with that AI and let them take the city or outpost controlling the Order of Asok; alternatively, if the Order of Asok is not inside a city, hope that the AI players you are at war with or some wandering monster comes by and destroys the improvement, at which point don't build on it again.

The things that apply for the Order of Asok also applies for the Mercenary Camps you can build on ?Border Villages, except that Knights of Asok could actually be decent units if it weren't for the excessive wages they receive whereas mercenaries and hunters would be garbage units regardless. So don't bother building Mercenary Camps, either (at least until the 1.1 patch, when mercenaries are supposed to lose their wages - they'll still be garbage units, but they at least will become free garbage units like the Wildings and Darklings are).

Wildings, however, do not receive wages and so can be used as free and crappy garrison units that artificially inflate your faction power, and there is no penalty for not disbanding them. If the reason you disband them is to take them out of the 'units needing to be moved' queue, you can do that by putting them into guard mode or stationing them in a city. If you're disbanding Wildings to protect your economy, don't bother - they don't cost you anything anyways.

Edit: Now that I think about it, if you have a spell that can destroy the resources on a tile, casting that spell on the location that the Order of Asok or other troop spawner is located could cause the troops to stop spawning, but this is an off button with no on button.

If you click on the recruiting camp, you will see a city name, that it is attached to.

If you go to details, on that city screen, you will see a list of improvements, each with an "X" beside it, which you can use to remove the improvement.

I have not tried this, with recruiting camps (I mostly use it to cripple threatened cities if I feel that I cannot defend them and will not be inclined to re-take them any time soon), so I do not know if you will be able to resume recruitment by rebuilding the improvement.

Edit: Cancel that -- I am not seeing them listed there.  You can always just disband the troops when they are recruited.  I think this winds up being a temporary boost to a cities growth.