tokio-rustls: Remove some feature

[quininer]

This MR removes some features that are not commonly used, so that anyone who wants to enable a feature can specify it by importing rustls crate directly.

[cpu]

anyone who wants to enable a feature can specify it by importing rustls crate directly.

It might be worth adding some text like this to the README. It would help people know you're not likely to accept PRs like https://github.com/tokio-rs/tls/pull/134

[quininer]

@cpu I added a note for Cargo.toml.

[cpu]

@cpu I added a note for Cargo.toml.

Good idea, that's a better place than the README. Thanks!

[djc]

I guess these changes are fine, but I prefer forwarding these. A side dependency like you're proposing feels pretty clunky to me -- rustls doesn't change features all that often, and tokio-rustls is a pretty tight wrapper around rustls.

[quininer]

My main motivation for want to remove it is that it lacks maintenance and import rustls is not hard. but I don't have a strong opinion, if someone is willing maintain it, then it can be kept.

[djc]

What do you mean by "lacks maintenance"?

[quininer]

Because no one is tracking and syncing it to keep it consistent with rustls. and there's no testing to guarantee it works. The reexport of webpki is also same problem.

[djc]

Hmm, I just don't see that many risks? I'm happy to add read_buf and secret_extraction features here to forward to rustls. (Did you see #138 already?)

(I agree that the reexport of webpki is probably less valuable, though I also don't see any real downsides.)

[quininer]

I don't have a strong opinion, I just don't see too many benefits.

Anyway if you are willing to maintain it, then let's keep it. we can release current version first, and then add new features at any time.