uucore: remove process functions

[xtqqczze]

Closes #12342

Remove wrapper functions from uucore::process and use rustix directly in each crate.

[sylvestre]

are you sure it isn't used by other consumers of uucore ?

[xtqqczze]

are you sure it isn't used by other consumers of uucore ?

nushell depends on uucore crate but not these functions, but other coreutils repos do:

https://github.com/uutils/procps/blob/4ebf73c7129c4ef637f2551690e8d72b861ff4f0/src/uu/pgrep/src/process.rs#L494

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/misc/io-errors is no longer failing!
Congrats! The gnu test tests/timeout/timeout-group is no longer failing!
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[sylvestre]

@xtqqczze still draft, no ? :)

[xtqqczze]

Downstream: uutils/procps#701

[codspeed-hq]

Merging this PR will not alter performance

✅ 319 untouched benchmarks
⏩ 46 skipped benchmarks¹

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_{Comparing xtqqczze:rm-getpid (3203759) with main (7ea1211)}

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:

Congrats! The gnu test tests/cp/link-heap is now passing!
Congrats! The gnu test tests/tail/tail-n0f is now passing!