ItemManager: Remove unused constant

It is obsolete since 83a2ad11d6
(2012-08-15, Item: replace arrays by vector.)

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Merge pull request #791 from stefanbeller/master

ItemManager: Remove unused constant
Fix namespace clash on round()
Merge pull request #792 from AMDmi3/round-collision

Fix namespace clash with ::round()