Remove outdated comment about std::hash::DefaultHasher being inaccessible

[dbdr]

Fixes #134717 (confirmed by @hkBst)

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[ibraheemdev]

It looks like this comment is outdated too.

[hkBst]

You are right. So should this entire module be unmoduled and inlined into another file?

[hkBst]

Why not just inline this into https://github.com/rust-lang/rust/blob/master/library/std/src/hash/mod.rs without mod wrapper?

[ibraheemdev]

Taking a closer look, I think the comments are actually correct. This module was added in #115694 for the reasons the comment mentions. I think we can confusion by mentioning that the types are re-exported elsewhere.

- //! Although its items are public and contain stability attributes, they can't actually be accessed
- //! outside this crate.
+ //! Although its items are public and contain stability attributes, they can't actually be accessed
+ //! through this module, and are instead re-exported from `std::hash` and `std::collections::hash_map`.

[hkBst]

I still think this comment is more confusing than enlightening, and best removed. It's a crate-private module with exports through https://github.com/rust-lang/rust/blob/master/library/std/src/hash/mod.rs.