Zabbix

........S. [ZBXNEXT-3480] optimized inventory value expansion

Moved the search for the inventory directly by using
the itemid.
Perform all the searches (item, host and inventory) directly
through the new DCget_host_inventory_value_by_itemid()
function.
Also, the change will copy only the desired field to the
destination without passing the whole inventoty structure.

I was thinking to keep the DCget_host_inventory_by_hostid()
function, but at this moment is not really useful, so remove it.