[TASK] Extbase-Repository: Use ClassNamingUtility from core

Use core-functionality for conversion of repository-name
to its model-name.

Change-Id: I2a3247dd05ea24f12d1c235d8bf39bebdfbdb9ff
Resolves: #63809
Releases: master
Reviewed-on: http://review.typo3.org/35345
Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>