This implementation is wrong in the sense of its semantics is not about
dereferencing a thin pointer to something, but just to give access to one
specific field of the entire structure. That's not how `Deref` is supposed to
be used.
Moreover, it creates conflict between the `SlidingSyncRoom.timeline` field,
and `SlidingSyncRoom.inner.timeline` field, which both exist, but not for the
same purposes. It creates confusion in the code.
Finally, it's better to expose proper getters to the outside world, so that we
control _and_ test _and_ know exactly what API we provide.
Ivan Enderlin
43f2f60bfd