Remove unused calendar backup

[ddongchul]

Hello and thank you for wanting to contribute to the MagicMirror² project!

Please make sure that you have followed these 3 rules before submitting your Pull Request:

1. Base your pull requests against the develop branch.
2. Include these infos in the description:

• Does the pull request solve a related issue?
• If so, can you reference the issue like this Fixes #<issue_number>?
• What does the pull request accomplish? Use a list if needed.
• If it includes major visual changes please add screenshots.

3. Please run node --run lint:fix before submitting so that
   style issues are fixed.

Note: Sometimes the development moves very fast. It is highly
recommended that you update your branch of develop before creating a
pull request to send us your changes. This makes everyone's lives
easier (including yours) and helps us out on the development team.

Thanks again and have a nice day!