Revert "tests: replace rlimit dependency with rustix::process"

[xtqqczze]

Address a build issue on Redox: #14664 (comment).

This reverts commit b60091b.

[sylvestre]

sorry but i am not going to revert anything until we have a CI running for redox

[oech3]

I think we don't need to revert this since we were not running test(impossible?) for Redox on the CI previously.

[xtqqczze]

I think we should add a check-only job at the very least:

cargo check --all-targets --features feat_os_unix_redox --target x86_64-unknown-redox

We can set continue-on-error: true for now so that any existing errors don’t block CI, while still giving us visibility into Redox build issues.

[sylvestre]

Sounds good