Removing a town is pretty simple, but it takes some patience. You start by deleting one and one building or road until you cant do it anymore, and then build trees on every tile within about 10-15 tiles from the city. Repeat these steps for a while, and you should be able to remove it completely. If you cant, you'll have to bribe the city council. To make it less risky, just save the game before bribing, and then load it if the city council busts you.

Happy town removing. =)