Bug 18936: (QA follow-up) Fix failing test in api/v1/holds.t

Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

t/db_dependent/api/v1/holds.t

@@ -315,7 +315,6 @@ subtest 'test AllowHoldPolicyOverride' => sub {
 
     Koha::CirculationRules->set_rules(
         {
-            categorycode => undef,
             itemtype     => undef,
             branchcode   => undef,
             rules        => {