Remove unused internal code

[duriantaco]

Hello,

Just doing some cleanup. Removed four internal items that are defined but never referenced anywhere in the codebase:

• matches_grammar() in parsing.py —> utility function with zero callers
• lib2to3_unparse() in parsing.py —> utility function with zero callers
• is_function_or_class() in nodes.py —> function with zero callers (note: is_parent_function_or_class nearby is still
  used)
• Deprecated in mode.py — warning class never raised or referenced

Verified with grep across all file types — each appears only at its definition.

Found during static analysis with Skylos.

Checklist

• Implement any code style changes under the --preview style?
• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

[github-actions]

diff-shades results comparing this PR (d5f8b53) to main (0dae20b):

--preview style: no changes

--stable style: no changes

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What is this? | Workflow run | diff-shades documentation

[duriantaco]

Removed the changes.md entry as per reviewer's request