fix: remove stale self reference from derive_host_configuration_inner doc comment (#532)

# 🔍 Description

Engineering cleanup. The doc comment on
`derive_host_configuration_inner` referenced "Take an immutable
reference to self" — a rationale that became inaccurate when the
function was refactored from a method to a free function taking
individual parameters.

# 🤔 Rationale

Stale comment flagged in [#529
review](#529 (comment)).
The bullet describing `&self` semantics no longer applies and was
misleading.

**Before:**
```rust
/// This is separated from `derive_host_configuration` to:
///
/// - Allow for easier testing since we can directly construct a COSI object
///   with the required fields without having to go through the GPT
///   population logic.
/// - Take an immutable reference to self, which makes it clear that this
///   function does not modify the COSI object and relies on all necessary
///   data being pre-populated. (Also simplifies borrowing.)
pub(super) fn derive_host_configuration_inner(
    source_url: &Url,
    ...
```

**After:**
```rust
/// This is separated from `derive_host_configuration` to allow for easier
/// testing since we can directly construct a COSI object with the required
/// fields without having to go through the GPT population logic.
pub(super) fn derive_host_configuration_inner(
    source_url: &Url,
    ...
```

# 📝 Checks

- [x] Check
[dev-docs/manual-validation.md](/dev-docs/manual-validation.md)

# 📌 Follow-ups

TODO:

- #0000

# 🗒️ Notes

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Author: Copilot

crates/trident/src/osimage/cosi/derived_hc.rs

@@ -21,14 +21,9 @@ use super::{metadata::Image, CosiPartitioningInfo};
 /// A helper function that performs the actual derivation of the host
 /// configuration assuming that the COSI version is sufficient and the
 /// necessary metadata and GPT data are present. This is separated from
-/// `derive_host_configuration` to:
-///
-/// - Allow for easier testing since we can directly construct a COSI object
-///   with the required fields without having to go through the GPT
-///   population logic.
-/// - Take an immutable reference to self, which makes it clear that this
-///   function does not modify the COSI object and relies on all necessary
-///   data being pre-populated. (Also simplifies borrowing.)
+/// `derive_host_configuration` to allow for easier testing since we can
+/// directly construct a COSI object with the required fields without having
+/// to go through the GPT population logic.
 pub(super) fn derive_host_configuration_inner(
     source_url: &Url,
     metadata_sha384: &Sha384Hash,