Add an INotifyKilled interface, which is what most things that used INotifyDamaged actually cared about.

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -57,6 +57,7 @@ namespace OpenRA.Traits
     public interface IOrderVoice { string VoicePhraseForOrder(Actor self, Order order); }
     public interface INotifySold { void Selling(Actor self); void Sold(Actor self); }
     public interface INotifyDamage { void Damaged(Actor self, AttackInfo e); }
+    public interface INotifyKilled { void Killed(Actor self, AttackInfo e); }
     public interface INotifyAppliedDamage { void AppliedDamage(Actor self, Actor damaged, AttackInfo e); }
     public interface INotifyBuildComplete { void BuildingComplete(Actor self); }
     public interface INotifyProduction { void UnitProduced(Actor self, Actor other, int2 exit); }