[CLEANUP] Code Cleanup EXT:form

Plenty of easy cleanups, a few more difficult ones
and removed dead code two times.

Resolves: #62903
Releases: master
Change-Id: Idbe0bee434e23a537f065d0bf19b55b0d5073713
Reviewed-on: http://review.typo3.org/34047
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>