[BUGFIX] Remove misspelled setting rootlevel for sys_file_collection

The correct setting would have been rootLevel. So it was never
evaluated, remove it.

Resolves: #59773
Releases: 6.3, 6.2, 6.1
Change-Id: I594924caed47c5c911def94524148354790b77b4
Reviewed-on: https://review.typo3.org/31012
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe