[TASK] Cleanup saltedpasswords extension configuration

Remove the note "Install tool has hardcoded md5 hashing,
enabling this setting will prevent use of a install-tool-created
BE user." for backend.BE.forceSalted

Resolves: #51355
Releases: 6.2
Change-Id: Ic6dd03d37f5c4fe1027dece048693c74ab4dc98e
Reviewed-on: https://review.typo3.org/23395
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Kai Ole Hartwig
Tested-by: Kai Ole Hartwig
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind