Docs: Remove unused imports in MDX documentation

[sitogi]

What I did

I removed the unused import Story from a code snippet in the MDX documentation.

How to test

1. Refer to MDX Documentation and create Checkbox.mdx .
2. Please confirm that the imported Story is unused and can be safely removed.

Checklist

Skipping because it is a documentation-only fix.

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[jonniebigodes]

@sitogi, thanks for taking the time to put together this pull request. Appreciate it 🙏 ! I've checked and we're good to go, this was a nice find. Once the checklist clears, I'll gladly merge it.

Hope you have a great day.

Stay safe

[sitogi]

Thank you for merging!