Using tonic for clients still pulls in extra dependencies

From my comment in https://github.com/hyperium/tonic/issues/959#issuecomment-1108264503:

> I finally tried using #960 and I don't think it's an adequate fix. First of all, the `tls` feature still pulls in `transport`, so by default if you pull in `tls` or one of the features that depend on it, you'll still get the server-side dependencies. That part can actually be worked around by depending on the other required features directly, but then I noticed that the entire `tonic::transport` module is unavailable if the `transport` feature is disabled, so I don't have access to things like `Error`, `Channel` or `Endpoint` from that module.
>
> Should I submit a PR replacing the use of `transport` internally with `channel` for client-side or both-side items?