Docs: Remove incorrect mention of .left- and .right- utilities from migration guide

[coliff]

Description

There are no classes in Bootstrap 4.x beginning with .left- or .right-.

(You can do a CTRL+F on https://cdn.jsdelivr.net/npm/bootstrap@4.6.2/dist/css/bootstrap.css to check)

Motivation & Context

Make the migration guide easier to follow. :-)

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-39054--twbs-bootstrap.netlify.app/

Related issues

[XhmikosR]

The CSS you are linking is from v5.3.1.

The message probably should read:

- Renamed `.*-left` and `.*-right` to `.*-start` and `.*-end`.

But if we list all of the renames, we might not need that sentence.

[coliff]

The CSS you are linking is from v5.3.1.

Oops, I edited my post. Bootstrap 4.x doesn't have any classes beginning with .left- or .right- so I think that sentence can be removed altogether. We list all the renames below anyway.