[TASK] Cleanup setting value $SET

For consistent usage the variable $SET was deleted 
and replaced with $this->setting.

Resolves: #83466
Releases: master
Change-Id: I6c5174515d430ee829943b457a80f568990a7859
Reviewed-on: https://review.typo3.org/55262


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>