Removes unused ci_text_for_status helper

What does this MR do and why?

This helper is not in used anymore so it can be safely removed.

Classes at lib/gitlab/ci/status/ can provide their own text on a case-by-case basis.

Part of #423029 (closed) as a clean up before making further changes.

Screenshots or screen recordings

NA

How to set up and validate locally

NA

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #423029 (closed)