7de5fe76f2
Remove unnecessary rustc_const_stable attributes.
These attributes were added in https://github.com/rust-lang/rust/pull/74033#discussion_r450593156 because of [std::io::lazy::Lazy::new](0c03aee8b8/src/libstd/io/lazy.rs (L21-L23)
). But [std::io::lazy::Lazy is gone now](https://github.com/rust-lang/rust/pull/77154), so this can be cleaned up.
@rustbot modify labels: +T-libs +C-cleanup