Delete existing wp-env config if latest version

[cadic]

Description of the Change

set-core-veresion.js script will delete existing .wp-env.override.json if 'latest' WordPress core version is specified.

Closes #5

Verification Process

1. Install npx github:10up/cypress-wp-setup
2. Set core version other than latest (f.e. ./tests/bin/set-core-version.js WordPress/WordPress#5.9)
3. Set core version to latest: ./tests/bin/set-core-version.js latest
4. .wp-env.override.json expected to be deleted

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

Fixed - Setting core version to latest after if other version was set before

Credits

Props @cadic