[BUGFIX] Fix generation of create action URLs in backend user module

The URLs to the create actions for backend users and backend groups were
built in a strange way which required some quirks to be fully functional.

This patch removes the unnecessary `explodeUrl2Array()` call, which also
renders the `rawurlencode()` obsolete.

Resolves: #85211
Releases: master
Change-Id: I3b8f5864fc398b9a4f8f2c0de5d72a38cb8a471b
Reviewed-on: https://review.typo3.org/57172


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Riccardo De Contardi <erredeco@gmail.com>
Tested-by: Riccardo De Contardi <erredeco@gmail.com>