sort: fix warnings about unused stuff on Redox

[cakebaker]

This PR fixes some warnings about unused imports and an unused function on Redox. See, for example, https://github.com/uutils/coreutils/actions/runs/23742274684/job/69162751126?pr=11495#step:17:282:

warning: unused imports: `AtomicBool` and `Ordering`
 --> src/uu/sort/src/tmp_dir.rs:5:25
  |
5 | use std::sync::atomic::{AtomicBool, Ordering};
  |                         ^^^^^^^^^^  ^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

warning: unused imports: `USimpleError`, `show_error`, and `translate`
  --> src/uu/sort/src/tmp_dir.rs:14:22
   |
14 |     error::{UResult, USimpleError},
   |                      ^^^^^^^^^^^^
15 |     show_error, translate,
   |     ^^^^^^^^^^  ^^^^^^^^^

warning: function `remove_tmp_dir` is never used
   --> src/uu/sort/src/tmp_dir.rs:184:4
    |
184 | fn remove_tmp_dir(path: &Path) -> std::io::Result<()> {

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/misc/io-errors is no longer failing!
Skip an intermittent issue tests/pr/bounded-memory (was skipped on 'main', now failing)

[codspeed-hq]

Merging this PR will improve performance by 4.63%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 303 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	cp_large_file[16]	278 µs	265.7 µs	+4.63%

---

_{Comparing cakebaker:sort_fix_warnings_on_redox (6d74ff7) with main (c7710ac)}

Footnotes

1. 46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/misc/io-errors is no longer failing!
Note: The gnu test tests/seq/seq-epipe is now being skipped but was previously passing.
Congrats! The gnu test tests/pr/bounded-memory is now passing!