[TASK] Remove backend user ID from workspace preview config

The configuration within `sys_preview` contained the
Backend User ID. Previously, until TYPO3 v9, this was
used to simulate a backend user with his/her permissions,
however this was changed with the introduction of Middlewares
and a custom PreviewUserAuthentication object.

This information does not need to be stored, as it hasn't
been evaluated anymore anyways.

Resolves: #88601
Releases: master
Change-Id: I2b3c4979f38a3c1343a0f5bff3c2bd762affc0e1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61108


Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Alexander Schnitzler <typo3@alexanderschnitzler.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Alexander Schnitzler <typo3@alexanderschnitzler.de>
Reviewed-by: Benni Mack <benni@typo3.org>