uucore: remove process functions

[xtqqczze]

Closes #12342

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

The last downstream consumer of these APIs was removed in uutils/procps#701.

In any case, migrating downstream users to rustix is straightforward, as the wrappers provide only a thin abstraction over the underlying process APIs.

[sylvestre]

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

[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 ? :)

[codspeed-hq]

Merging this PR will not alter performance

✅ 139 untouched benchmarks
⏩ 272 skipped benchmarks¹

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_{Comparing xtqqczze:rm-getpid (60cd47e) with main (b7519db)}

Footnotes

1. 272 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:

GNU test failed: tests/cp/parent-perm-race. tests/cp/parent-perm-race is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
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/dd/no-allocate is now being skipped but was previously passing.

[oech3]

This is one of a large disadvantage of public thin wrappers...

[oech3]

@sylvestre I'd like to have this before #13006

[oech3]

Conflicting