Remove the never type documentation

[Havvy]

It's still not stable. :(

[ehuss]

FWIW, there was a renewed effort at rust-lang/rust#79470 to attempt to stabilize it.

I don't think it should be removed, because it is stable as a function return type.

[Havvy]

Its usage there is not as a type, but as a stand-in for not return a type.

I wonder how long it'll be until it can be actually stabilized.

[crlf0710]

Maybe, instead of removing, we can mark them as nightly-only and strip or gray them out when building the reference for stable Rust. For the people doing their daily work on nightly Rust, maybe it's worth giving them a version of reference for the broader language.

[Havvy]

That's supposed to be the purview of The Unstable Book. Otherwise, trying to document things that are going to change is a lot of churn and we don't have the manpower for that.