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

Resolves: #58271
Releases: 6.2
Change-Id: I14583a1c44d881ab0b7ce241716eab9decba1acc
Reviewed-on: https://review.typo3.org/29691
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen