[TASK] Make use of .t3-table in EXT: beuser

Use <table class="t3-table"> in backend module.

Change-Id: I695587a4ec3ccdb4b6170063fd373c575efb5e70
Resolves: #52568
Releases: 6.2
Reviewed-on: https://review.typo3.org/24439
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn