[TASK] Remove find file in EXT: lowlevel

Removes the find file function from EXT: lowlevel.
Find file was only available for admins.

Change-Id: I79cedeeef8e8cea9266c893a2c9bd2ab462be482
Resolves: #55134
Releases: 6.2
Reviewed-on: https://review.typo3.org/26928
Reviewed-by: Oliver Klee
Reviewed-by: Ernesto Baschny
Tested-by: Ernesto Baschny
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters