[TASK] Remove unused code in ReferenceIndex

An unused elseif() constraint is removed from ReferenceIndex
which cannot be called technically.

Resolves: #77361
Releases: master
Change-Id: Ie63f2b8566a98eff5322b8e95f42b4c7ca83896a
Reviewed-on: https://review.typo3.org/49323


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Sebastian Bumann <bumann.sebastian@gmail.com>
Tested-by: Sebastian Bumann <bumann.sebastian@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>