[TASK] Cleanup for ClassNamingUtility

Small cleanups for the new feature
which just got merged.

Releases: 6.1
Fixes: #43052
Change-Id: I9c7df202f7e63c148f35fefe30e134b0a299b124
Reviewed-on: https://review.typo3.org/18189
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring