[BUGFIX] Add confirm dialog on delete again

In the backend user module, the delete icon shows again a confirm modal to
prevent accidently deleting a backend user.

Resolves: #75994
Releases: master, 7.6
Change-Id: I066f94237301eb923ac982fdacb5566c396a5e43
Reviewed-on: https://review.typo3.org/47979


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>