[TASK] Simplify propertyName-creation

Since PHP 5.3.0 function lcfirst() exists.

Resolves: #47171
Releases: 6.0, 6.1
Change-Id: I314ee3c14683283dc000daad41693294c12c62d2
Reviewed-on: https://review.typo3.org/19870
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer