Allow duplicate drops for the same mob

This previously caused a bunch (327 to be exact) of drops to silently not be inserted due to "INSERT _IGNORE_ INTO drop_data (...)"

src/main/resources/db/009-drop.sql

@@ -8,7 +8,6 @@ CREATE TABLE lb_drop_data
     questid          INT    NOT NULL DEFAULT '0',
     chance           INT    NOT NULL DEFAULT '0',
     PRIMARY KEY (id),
-    UNIQUE KEY (dropperid, itemid),
     KEY mobid (dropperid),
     INDEX (dropperid, itemid)
 );