[BUGFIX] Remove wrong storage->isPublic() check in localFolderTree

In localFolderTree->ext_isLinkable() is a check for storage->isPublic()
but the isPublic flag has nothing to do with the fact if links
to the files can be created.

This change removes this check.

Resolves: #56183
Releases: 6.2
Change-Id: Ia0e264b46259c0bd284a789a4eab48cf9a9e3b14
Reviewed-on: https://review.typo3.org/27772
Reviewed-by: Wouter Wolters
Reviewed-by: Sebastian Fischer
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter