Bug 14325: Test calls C4::Context::set_userenv

Bug 14325: Test calls C4::Context::set_userenv

This is a case of works by accident. This patch corrects the
set_userenv call.

TEST PLAN
---------
1) prove t/db_dependent/Borrower_Discharge.t
   -- works
2) git grep :set_userenv
   -- only this one file.
3) Confirm the the C4/Context.pm has a set_userenv
   which shifts the first parameter, as intended for
   a -> call and not a :: call.
4) apply patch
5) prove t/db_dependent/Borrower_Discharge.t
   -- still works
6) git grep :set_userenv
   -- nothing now.
7) run koha qa test tools

Signed-off-by: Indranil Das Gupta (L2C2 Technologies) <indradg@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>