Bug 23916: (follow-up) Fix unit test

Bug 23916: (follow-up) Fix unit test

This commit responds to the comment made by Katrin in comment #73. I
have removed the lines cited as causing the contraint violation. The
were added in the original iteration of the bug patches and, despite
spending time trying to get to the bottom of it, I cannot figure out
why. There are no changes in the patchset relating to Koha/Patron.pm and
removing the lines does not cause any of the tests in files that *are*
affected by this patchset to fail. I do not know why these lines were
ever added in the first place, unfortunately I did not add comments
explaining (lesson learned)!

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>