Any usage of FontAwesome has been removed with #97877 already. This
patch removes the integration of FontAwesome from the TYPO3 backend,
including the `FontAwesomeIconProvider`, the font files, and any CSS.

The polyfill extension is available via Composer via
```
composer require friendsoftypo3/fontawesome-provider
```
and in the TER soon.

Resolves: #98089
Related: #97877
Releases: main
Change-Id: I28968bc45a43a244b82fe9a888e10d958d42cf1a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75342


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>