removed bootstrap-4 from footer

[AKSHAY-CHOWDARY]

Description

Removed boostrap-4 from footer #40923

Motivation & Context

Now that it's been nearly 2 years since Bootstrap v4 went EOL I think it makes sense to remove that link as having it there may indirectly wrongly give the impression that it's supported and/or recommended in some way.

Removing this link may help reduce page rank of Bootstrap v4 pages in search engines and prioritize v5 too :-) (searching for bootstrap carousel in Google for me still shows the v4.0 docs as the top result

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-{your_pr_number}--twbs-bootstrap.netlify.app/

Related issues

[julien-deramond]

Thanks @AKSHAY-CHOWDARY but there's already a PR for that, see #40924