[BUGFIX] Fix localization of the BE user module

Fix some hardcoded labels by replacing them with
f:translate tags.

Change-Id: Ic75f7bd021ff8353b7709906859d2c02eb452b23
Resolves: #49402
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/21724
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind