[BUGFIX] Show correct record title for be_groups and be_users

Currently it lists groups only using field title of
be_groups table regardless of any label definitions in TCA.
Use BackendUtility::getRecordTitle() instead.

Change-Id: I051c29687cb51d1883846b3cb780409c1e1cadc4
Resolves: #34631
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/22374
Reviewed-by: Markus Klein
Tested-by: Markus Klein