[TASK] DatabaseRecordList: Drop property `fixedL`

The property `fixedL` was only used once (see `ElementBrowserRecordList`,
`BackendUtility::getRecordTitlePrep`). The removal of the second
parameter `fixedL` in `getRecordTitlePrep` hasn't changed the behaviour,
as the backend user's UC `titleLen` is used as default constraint anyway.

Therefore, the property `fixedL` has been removed.

Releases: master
Resolves: #92114
Change-Id: Ib15a268e3c81f72737a310c71fc3800b13288c30
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65470


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>