security(swift): remove placeholder SSE module (backlog#646)
The Swift `encryption` module was a non-functional stub: `encrypt_data`
returned the plaintext unchanged while labeling it AES-256-GCM in the
object metadata, and `generate_iv` derived the IV from a timestamp
rather than a CSPRNG. It had no production caller (only a `pub mod`
declaration and one integration test), so wiring it in as-is would have
silently shipped plaintext advertised as ciphertext.
We are not supporting Swift server-side encryption for now, so remove
the module outright rather than keep a dangerous stub around:
- delete crates/protocols/src/swift/encryption.rs
- drop `pub mod encryption;` from swift/mod.rs
- remove the encryption case (and unused import) from the swift
integration test
The module reached main dubiously: it was introduced together with the
whole Swift API in commit 86e93624 ("fix(heal): canonicalize scanner
object-dir repairs (#3864)"), a 1665-file squash whose PR description
only covered the heal change and never mentioned Swift or SSE.
Verified: cargo fmt; cargo test -p rustfs-protocols --features swift
--test swift_simple_integration (10 passed); arch guardrail scripts pass.
Zhengchao An