[TASK] Backend user management: add delete button

Add remove button in the backend users list with
a confirmation dialog.

Resolves: #43053
Releases: 6.2
Change-Id: I5bffc18c4aabdcc597094f4b173c187e8c8ccac2
Reviewed-on: https://review.typo3.org/21591
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe