[TASK] Use DataHandler testing framework for simple import test

Adapt the impexp simple import test to the testing framework
available with #54855.

Resolves: #55664
Related: #54855
Releases: 6.2
Change-Id: I6f1e9eb6ef3bda5b984ac67af3964fed90ba41f2
Reviewed-on: https://review.typo3.org/27325
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Marc Bastian Heinrichs
Tested-by: Marc Bastian Heinrichs