Remove unnecessary stuff in boosted-*.scss files

[MewenLeHo]

Related issues

Closes #2153

Description

Remove unnecessary stuff in boosted-grid.scss

Motivation & Context

Lighter code and smaller bundle size.

Types of change

• Bug fix (non-breaking which fixes an issue)

Live previews

• https://deploy-preview-2196--boosted.netlify.app/

Checklist

Contribution

• I have read the contributing guidelines

Accessibility

• (NA) My change follows accessibility good practices; I have at least run axe

Design

• (NA) My change respects the design guidelines defined in Orange Design System
• (NA) My change is compatible with a responsive display

Development

• My change follows the developer guide
• (NA) I have added JavaScript unit tests to cover my changes
• (NA) I have added SCSS unit tests to cover my changes

Documentation

• (NA) My change introduces changes to the documentation and/or I have updated the documentation accordingly

Checklist (for Core Team only)

• My change introduces changes to the migration guide
• (NA) My new component is well displayed in Storybook
• (NA) My new component is compatible with RTL
• (NA) Manually run BrowserStack tests
• (NA) Manually test browser compatibility with BrowserStack (Chrome >= 60, Firefox >= 60 (+ ESR), Edge, Safari >= 12, iOS Safari, Chrome & Firefox on Android)
• Code review
• Design review
• A11y review

After the merge

• Manually launch Percy tests

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[MewenLeHo]

No difference spotted for boosted-reboot.scss vs. bootstrap-reboot.scss.
boosted-reboot.css is bigger but we have more variables so it seems pretty normal.

[louismaximepiton]

LGTM, great to have this!

[MewenLeHo]

Note: we decided to go closer to Bootstrap by incorporating the following commit twbs/bootstrap@5ac9fe8

[julien-deramond]

LGTM, good job!