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

Resolves: #58269
Releases: 6.2
Change-Id: I98bd23c3625c5807f2de3c8b2c3d9389c2a02c6c
Reviewed-on: https://review.typo3.org/29689
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen