[CLEANUP] Cleanup \EBT\ExtensionBuilder\Domain\Model\DomainObject

Resolves: #58275
Releases: 6.2
Change-Id: I4d97da8af79c3ca261d1e4db56b7a93347a8add5
Reviewed-on: https://review.typo3.org/29715
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen