[!!!][TASK] Remove "TCEforms" wrapper in FlexForm definitions

In order to further simplify FlexForm definitions,
the superfluous array key "TCEforms" is now removed
and not evaluated anymore. Its sole purpose was to
wrap real TCA definitions.

The automatic removal of this key was already done
in FormEngine context. This is now always done, when
parsing FlexForm definitions with FlexFormTools
(parseDataStructureByIdentifier).

Resolves: #97126
Releases: main
Change-Id: Ib27fd7025e0c21cbd4879454f8dc9dd548256b7c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73835


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>