chore: Revert Flashbar fixes

[jperals]

Description

A bug in old versions of postcss-calc is causing some third party packages to fail when trying to minimize the CSS. We need to revert two commits until we are able to work around that issue by refactoring the SCSS code to use less nested expressions.

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

Base: 93.30% // Head: 93.30% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (30a5d5a) compared to base (bc541ba).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #787      +/-   ##
==========================================
- Coverage   93.30%   93.30%   -0.01%     
==========================================
  Files         585      585              
  Lines       17141    17135       -6     
  Branches     4732     4726       -6     
==========================================
- Hits        15994    15988       -6     
  Misses       1067     1067              
  Partials       80       80              

Impacted Files	Coverage Δ
src/app-layout/index.tsx	95.06% <ø> (ø)
src/app-layout/visual-refresh/notifications.tsx	100.00% <ø> (ø)
src/app-layout/notifications/index.tsx	100.00% <100.00%> (ø)
src/flashbar/collapsible-flashbar.tsx	97.90% <100.00%> (-0.06%)	⬇️

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