[TASK] Make use of "use"-statement for BackendUtility

Change-Id: I5d631cf408758e89c69b129bb414d1ee14289bdd
Resolves: #51158
Releases: 6.2
Reviewed-on: https://review.typo3.org/23182
Reviewed-by: Kai Ole Hartwig
Tested-by: Kai Ole Hartwig
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn