The previous commit gated `prune_older_than_keeps_fresh_files_drops_stale_ones`
on `#[cfg(unix)]` because the mtime-backdate helper relies on
`utimensat`, which doesn't exist on Windows. That left the
`#[cfg(not(unix))]` stub of `filetime_set_modified` with zero callers
on Windows, and `-D dead-code` (implied by `-D warnings`) refused to
compile the test binary on Windows runners.
Drop the Windows stub entirely. The `cfg(unix)` test is the only
caller; `cfg(not(unix))` builds need nothing in its place.
Restores PR #519 Windows CI to green.
Hunter Bown
2cfcca471e