If it is for sure a wart, it will eventually go away. But it may get much larger, and he may get a lot more of them before they fade away. There is a wart vaccine that your vet can sell you. Have to give it two or three times and it may or may not work.
If the unsightliness is bothersome, you can, with a gloved hand grab ahold of it, give a little twist and then quickly yank it off. (Assuming that you have him hog-tied or in a headgate at this time.) Most of them will have a thin stalk and will pull free easily. Expect some bleeding. "Blood Stop" powder and some pressure will stop it.
If it does not have a thin stalk/attachment and/or it does not pull free easily, then you should let a vet remove it due to the potential for excessive bleeding if it has to be cut off/out.
Some old-timers say that if you make them eat one of the warts, it will cure the problem.
