[TASK] Remove obsolete property from TypoScriptFrontendController

Left over unused protected property from #100998

Resolves: #101063
Related: #100963
Related: #100998
Releases: main
Change-Id: I431a42e118356c86d254f97612eae456ee9b8f83
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79380


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>