[TASK] Remove redundant type casts in ext:form

Some type casts in ext:form are superfluous, since it is
already ensured, that the variable type is as expected.

This change removes all redundant type casts.

Resolves: #102840
Releases: main
Change-Id: I0daa178ab69c88e61bc92f31caefd9f8b45766df
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82461


Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>