[FOLLOWUP] Fix override field handling in form engine

Remove duplicate code.

Resolves: #66705
Releases: master
Change-Id: Ib38862f30f85f7528166c7c3597fe2357dfa50f2
Reviewed-on: http://review.typo3.org/39169


Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>