Docs: Remove unnecessary href and tabindex="-1"

[louismaximepiton]

Description

Remove unnecessary href and tabindex="-1". The ones remaining in the buttons and in the interactions seem pretty legit for me.

Motivation & Context

Coherence inside the doc.

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
• (NA) I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-38196--twbs-bootstrap.netlify.app/docs/5.3/components/placeholders#example

Related issues

NA