* Remove unused dependencies
Inspired by #6938 ran `cargo +nightly udeps --features extra`.
Removes 2 crates and should remove an unnecessary intra-workspace
dependency which might open up further opportunities for compilation.
* Make windows-only dependency conditional in toml
`omnipath` is only used on Windows and already behind a `#[cfg]` block
in the code. Made the dependency in `Cargo.toml` conditional as well.
* Make `nu-pretty-hex` example a proper example
This allows making `rand` a dev-dependency in this crate.
