This method does the exact opposite of SetCallbacks -- unsubscribes the given instance from the callbacks --, although it might have some design issues.

The reason I need this is to be able to make a global input manager instead of having several instances of a generated class all over my code. A global input manager should make it easier to control action maps. However, to do this, I need to be able to unsubscribe classes from the events in OnDisable. Right now, we can just disable the action map in the instance, but there's no practical way to unsubscribe from the events.

Actually, now that I think about it, there might not actually be many problems with it. I might try to implement it myself.