[TASK] Replace GU::getIndpEnv('TYPO3_SITE_URL')

The information is available in the request and should be used from there.

Resolves: #94632
Releases: master
Change-Id: I8730e8a96bed7272d6c6239b7d55ea56a03bd2de
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70065


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>