[TASK] Deprecate BackendUtility::getPidForModTSconfig()

Removing cruft from BackendUtility is always fun. This time an
internal marked one-liner that is used only once bites the dust.

Resolves: #84994
Releases: master
Change-Id: Iaadbcf3dc74f329f91f1a48ba4096e8ea96f60a4
Reviewed-on: https://review.typo3.org/56955


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>