🐛 Bug: Transition mode should delete/rename .yml files to .yaml

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled in the newest version of the project.
• I have searched for related issues and found none that matched my issue.

Expected

Back in #2309 -> #2310, linting for YAML file extensions changed the preference from .yml to .yaml. Running CTA in transition mode (npx create-typescript-app) in an existing repository should migrate existing .yml files to .yaml

Actual

It does not. You end up with both .yml and .yaml files, and a bunch of lint complaints about the two of them.

Additional Info

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