server::conn::http1::Connection always holds a proto

[bossmc]

In the recent work to split the server::conn::Http into protocol-specific halves, the author of that change left the inner proto in an Option (and left a comment asking if this was needed any more). This used to be needed as part of the fallback processing (allowing the fallback to take() the HTTP/1 proto and break it into Parts in order to rebuild the HTTP/2 proto).

Now, since we're definitely using HTTP/1 we can just store the proto directly and, in the process delete a bunch of unwrap calls 💯. We need to be able to take the HTTP/1 Connection in a few places (when an UpgradeableConnection is upgraded for example) but we can scope down the places where we have to unwrap an Option that's almost always Some.

I also tidied up a few instances of dead code (some are feature-specific) which I ran into when running cargo test over this change.

[seanmonstar]

Thanks for cleaning this up! <3