[TASK] Remove deprecated form setup mixins

Form mixins were deprecated with #89742. The patch removes the code.

Resolves: #94861
Releases: master
Change-Id: Ic82729ae52d3f8c6ca7cd0ad8f6c97aceebc96d0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70528


Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: waldhacker <hello@waldhacker.dev>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: waldhacker <hello@waldhacker.dev>