Deprecate Session.set_window_status_async

[jwortmann]

There is also the newer Session.set_config_status_async which does basically the same thing, and there is no point in having two methods doing the same.

set_config_status_async is nicer because it prints the status message directly after the config name in brackets, so it's clearer that this message belongs to the LSP server.

At a later time we could remove the method bodies of the two deprecated methods (replace with pass).