🚀 Feature: Hydration should remove existing .md files from root directory if they are newly added to .github/

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Some repositories put files like CODE_OF_CONDUCT.md in the root of the repository. Some repositories put them in the .github/ directory. Either is fine: https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/adding-a-code-of-conduct-to-your-project / https://stackoverflow.com/questions/60507097/is-there-an-overview-of-what-can-go-into-a-github-dot-github-directory..

#441 added a "hydration" script that sets up an existing repository with this template's files. It creates files like .github/CODE_OF_CONDUCT.md but doesn't check whether those files already existed in the root directory. Let's add logic to delete any existing root directory equivalents.

Additional Info

No response