Deprecate Async apis

Deprecated Async apis.

I've not changed the `BaseChefContextLiveTest` to extend from `BaseApiLiveTest` because the `ChefContext` is used to access the `Json` and `ChefService` stuff.

We could refactor the tests to get those classes from another source and make the tests extend `BaseApiLiveTest`, but to work, that would also require changes to the `HostedChefApi` and `PrivateChefApi` hierarcy to make them extend from `ChefApi`, and I would prefer to don't change that in 1.6. (Any advice is welcome if this is a must).