[TASK] Avoid setting undefined property in test case

With PHP 8.2 setting undefined properties in class
instances is deprecated and emits corresponding
deprecation notice.

This patch removes a superflous test, setting a
undefiend property in `TypoScriptFrontendController`
to avoid PHP 8.2 deprecation message.

Resolves: #98039
Releases: main, 11.5
Change-Id: I0944a13f6c87c95db01577dbdb499c39675691be
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75313


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>