[FOLLOWUP][TASK] Remove deprecated output-related code from EXT:backend

Some occurrences of `->getVersionSelector()` were left.
These are removed now.

Resolves: #80705
Releases: master
Change-Id: Ifb47df09a35bfd355be450042978356c7336fa7e
Reviewed-on: https://review.typo3.org/52522


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>