[TASK] Remove unused SystemInformationToolbarItem->getDatabaseConnection

Since the introduction of doctrine getDatabaseConnection in
SystemInformationToolbarItem is no longer used and can be removed.

Resolves: #76354
Releases: master
Change-Id: I675ada2355bfe48b93de66cea03a3f0fc290d382
Reviewed-on: https://review.typo3.org/48365


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>