[TASK] Doctrine: Migrate admin_get_fields() in Typo3DbBackend

Migrate the call to admin_get_fields() in Typo3DbBackend

Resolves: #77612
Releases: master
Change-Id: I447bf1de213145a08fd671d7fc743643b0b4d582
Reviewed-on: https://review.typo3.org/49560


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>