Bug 20074: (follow-up) Remove another remainder of biblio hidden logic

Bug 20074: (follow-up) Remove another remainder of biblio hidden logic

Script authorities.pl still contains a module 2 calculation on the hidden
attribute, although it is used as a boolean.
Since -5 mod 2 == 1, it does no harm, but we better remove it.

Test plan:
Edit and save an authority. Verify that everything still works as expected.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>