[CLEANUP] Remove unused [BE][usePHPFileFunctions] option

Resolves: #57921
Releases: 6.2
Change-Id: I5342f0d4f78831605c24b3354c1fbb7316738ca4
Reviewed-on: https://review.typo3.org/29470
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind