tr: word the -ds missing-operand hint the way GNU does

[Socialpranker]

Split out of #14400 as requested there.

$ tr -ds a-z
tr: missing operand after 'a-z'
Two strings must be given when both deleting and squeezing repeats.   # GNU
Two strings must be given when deleting and squeezing.                # uutils, before

The second line of tr-error-missing-operand-deleting-squeezing now reads the way GNU prints it. The fr-FR string is reworded to match. The existing test_delete_and_squeeze_one_set assertion is updated.

GNU behavior established by running the installed GNU coreutils 9.11 binary (gtr) as a black box; I did not read GNU source.

Testing

• cargo test --no-default-features --features tr --test tests test_tr: 160 passed, 0 failed.
• cargo fmt --check: clean.

Disclosure

Prepared with AI assistance (Claude Opus 5.5, via Claude Code), per the AI policy in CONTRIBUTING.md. All testing was run locally.

[anastygnome]

GNU has been updated, can you retest

[github-actions]

GNU testsuite comparison:

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