De-document styling of warnings text

[rolandwalker]

Description

De-document styling of warnings text, by removing the relevant entries from myclirc and amending the changelog.

Motivation: there are some unexplored bugs in applying styling to warnings text elements, and it is better for main to stay releasable.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

No blocking findings in the PR diff (e14c630c...7087c76).

• Correctness/regressions: No functional code paths changed; only docs/sample config entries and changelog wording were updated.
• Security: No security-impacting changes.
• Tests/edge cases: No new test gaps introduced by this docs-only change.

Residual risk to track separately: warning-style keys are still present in runtime style mapping/code paths, just undocumented, so existing users with warnings.* overrides may still hit the underlying unresolved bugs.