Docs: drop unused icons

[julien-deramond]

Description

Drop unused icons in the project.

• Based on d70b5db, dropped arrow-right-short which is now used only in examples that declare the SVG on top of the files. So arrow-right-short is not used anymore in the rest of the documentation
• In the same spirit, I've checked all the site/layouts/partials/icons.html. Everything's used except maybe list; I don't think it is used but I was too afraid to have a regression (searching "list" in our project is a nightmare).
• While I was checking it, I also checked unused icons on top of the examples. Here are the lists of modified examples that need to be double-checked while reviewing this PR for non-regression:
  • Breadcrumbs
  • Buttons
  • Features
  • Jumbotrons
  • List groups
  • Modals
  • Sidebars

Motivation & Context

Lighten our files.

Type of changes

• Refactoring (non-breaking change)

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

Live previews

• https://deploy-preview-38103--twbs-bootstrap.netlify.app

[mdo]

Thanks!