Bug 16741 - Remove dead code "sub itemissues" from C4/Circulation.pm

Bug 16741 - Remove dead code "sub itemissues" from C4/Circulation.pm

To verify:
- git grep itemissues
Result: Appears in C4/Circulation.pm only

To test:
- apply patch
- git grep itemissues
Expected result: No occurences
- prove t/db_dependent/Circulation.t
Expected result: Pass OK

Signed-off-by: Claire Gravely <c.gravely@arts.ac.uk>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 97552074f028eefe81d27a4cba681bd5f0f1cd95)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>