RELEASES.md section for 1.10 contains an entry concerning a nightly feature

[jplatte]

concat_idents! is unstable to this day, but RELEASES.md has this to say about Rust 1.10:

Allow concat_idents! in type positions as well as in expression positions.

The release notes shouldn't really be talking about changes to unstable features, right?

[Mark-Simulacrum]

Yes, they shouldn't be, this was likely just an oversight at the time. We would be able to accept a PR nixing the entry, I think, even if there's probably not much point (given that 1.10 is quite old at this point).