Chop AddrStream out completely

[seanmonstar]

The AddrStream type can just go. Get out of here. Gone. It provides no benefit over tokio::net::TcpStream.

[oddgrd]

Hi! I'd like to start contributing to this project, and this issue looks like a good place to start. I'm a bit of a rust and OSS noob, so I may need some guidance even though it should be easy.