Revisit (or remove) `tbl_connect`

[nealrichardson]

Having a lazy object that lets you build a query and then only request from the API the things you need is a nice idea, but it's currently not fleshed out enough to be useful, and it's not clear that the Connect API currently supports enough server-side filtering to make this worthwhile. At some point we should either make a push to do this for real, or we should just delete it.