[FOLLOWUP][BUGFIX] Make category tree filterable for editors

Check if TCEFORM.pages.categories.config.treeConfig.rootUid
itself is in the users category mounts (no need for a pseudo
parent category)

Resolves: #83257
Releases: master,8.7,7.6
Change-Id: I8a60860ee3a22d68964f4e44018f0962f7f0f278
Reviewed-on: https://review.typo3.org/54978


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>