build: use "selinux" instead of "feat_selinux" feature name

[xtqqczze]

Do not specify feat_selinux in individual crates; it is now only defined at the workspace level.

cc: @cakebaker

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/tail-n0f (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.

[oech3]

coreutils/README.md

Lines 123 to 126 in bd908f0

	To build SELinux-specific features, including `chcon` and `runcon`, ensure that `libselinux`
	and `libclang` are installed on your system. Then, run the following command:
	```
	cargo build --release --features unix,feat_selinux

[oech3]

why test only?

[xtqqczze]

@sylvestre could you please review?

[codspeed-hq]

Merging this PR will improve performance by 7.8%

⚠️ 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
✅ 338 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	complex_relative_date	147.6 µs	136.9 µs	+7.8%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing xtqqczze:selinux (7f37c3c) with main (65957d9)}

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. ↩