[CLEANUP] Cleanup of method updateRefIndexTable

Limit the selected SQL fields to hash value only, since this
is sufficient for the processing. Use a boolean value for
$currentRelations to reduces memory footprint.

Resolves: #80207
Releases: master, 8.7
Change-Id: I323fa797b221c915848fc63cef78fb752a55ea26
Reviewed-on: https://review.typo3.org/51989


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Henrik Elsner <helsner@dfau.de>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>