[BUG] sys_file_reference: missing exclude fields for Non-Admins

Currently, only link, but not description and alternative
is a exclude field. So the others are ALWAYS visible.
They need to be adjusted as well.

Releases: 6.1
Resolves: #43939
Change-Id: I47ed483c81dc354ad3d8f13ad1029c77c920a0e4
Reviewed-on: https://review.typo3.org/19207
Reviewed-by: Felix Nagel
Tested-by: Felix Nagel
Reviewed-by: Tom Ruether
Tested-by: Tom Ruether
Reviewed-by: Andreas Wolf
Tested-by: Andreas Wolf