I/O plugin Controls are destroyed with ~IOPlug, however
Session::destroy()'s call to drop_references() still
triggers AutomationControl::session_going_away() on the
binding proxy.
This is even properly documented in session_object.h:
> A named object associated with a Session. Objects derived
> from this class are expected to be destroyed before the
> session calls drop_references().
947e6c7815