Core/Spell: Reset threat to zero when the hunter use Feign Death

Port From (https://github.com/TrinityCore/TrinityCore/commit/a8e4add6cc7de723ea8951743b17c894aacd3b8b)

Source/Game/Spells/Auras/AuraEffect.cs

@@ -1652,6 +1652,9 @@ namespace Game.Spells
                     }
                 }
 
+                foreach (var pair in target.GetThreatManager().GetThreatenedByMeList())
+                    pair.Value.ScaleThreat(0.0f);
+
                 if (target.GetMap().IsDungeon()) // feign death does not remove combat in dungeons
                 {
                     target.AttackStop();