[TASK] Clean up various options in UserAuthentication

This change adapts some comments
and makes the usage of "uc" clearer in various
places.

In addition, one change is removed where the session
data was checked against a non-hashed identifier, which
can now safely be removed in TYPO3 v12.0.

Resolves: #96825
Releases: main
Change-Id: Ib142168bd8fc248fc030d0f486d51a6fdbf23212
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73418


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>