[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/19039
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack