uucore/clap_localization: use iterator from lines()

[cakebaker]

This PR uses the iterator from lines() directly instead of collecting into a Vec. It also moves std::process::exit(0); outside a match as it is used in both arms.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)