Bug 17249: Remove GetKohaAuthorisedValuesFromField - (follow-up) inventory

Bug 17249: Remove GetKohaAuthorisedValuesFromField - (follow-up) inventory

Before this patch set, the tests in
t/db_dependent/Items/GetItemsForInventory.t were executed in 4s. But
with the previous patch, it was in 45sec(!)
To make sure decrease this execution time to what it was before, this
patch introduces a local to avoid the same query to be executed several
times.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>