[!!!][TASK] Remove deprecated code in SiteLanguage

Removed the following public methods:
* \TYPO3\CMS\Core\Site\Entity\SiteLanguage->getTwoLetterIsoCode
* \TYPO3\CMS\Core\Site\Entity\SiteLanguage->getDirection

Resolves: #101112
Related: #100963
Related: #99905
Related: #99908
Releases: main
Change-Id: I15374e397a3fd3ebb2bede2d02d2f835104bcb0c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79451


Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>