Bug 16428: [QA Follow-up] Useless call to GetMarcStructure in _build_default_values_f...

Bug 16428: [QA Follow-up] Useless call to GetMarcStructure in _build_default_values_for_mod_marc

The routine calls GetMarcStructure and does not use its return value
after all.

Test plan:
Run t/db_dependent/Items.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 6a706b86a273672b1e1ca3f1456fde08dd7a0da2)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
(cherry picked from commit b31ee2eaf9dd86171cac1598f3f9a611ea145f83)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>