"static" feature turns on native-tls even when it isn't wanted

The "static" trait in tor-rtcompat turns on native-tls/vendored.

That was fine before we added rustls support, but now it's wrong: it will make us turn on native-tls even if we didn't want it.

We should resolve this somehow; it may also require a solution at the level of the arti and arti-client crates.