[TASK] Small cleanup in Boostrap.php

Code cleanup prior to #41596
Releases: 6.1, 6.0

Change-Id: I87294a52e282175b345ee8b1a735604f6993e0f3
Reviewed-on: https://review.typo3.org/19038
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Marcus Schwemer
Tested-by: Marcus Schwemer
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack