doc(modules): Remove module style recommendation

[ranger-ross]

I was having a conversation about Rust modules with one of my coworkers who is relatively new to Rust.
They mentioned that using foo/mod.rs is not recommended in the Rust reference which surprised me.

Even in modern Rust, I still find the foo/mod.rs style much more common than using the "newer" style of adding foo.rs and adding a foo/ directory.

I think its worth removing this recommendation from the reference to make it unopinionated and avoid confusing newcomers.

[ehuss]

We recently revisited this here and decided to keep the existing text.

[ranger-ross]

Ah I see, given this has already been discussed, closing.