[BUGFIX] Consider all elements in typo3temp/assets/ when clearing

Only first level elements were considered when clearing assets in
typo3temp/assets/ using corresponding functionality in maintenance
section of the TYPO3 install tool.

Resolves: #89569
Releases: master, 9.5
Change-Id: I9237aa3c6200b57cf4da256531b25062f52708ee
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62179


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Susanne Moog <look@susi.dev>