boss timers plugin: change to use npc despawn event

Since e915070 it is possible to check hp in the despawn event.

This also fixes timer accuracy some since the timer starts at the time the npc despawns and not when the death animation starts.

runelite-client/src/main/java/net/runelite/client/plugins/bosstimer/BossTimersPlugin.java

@@ -28,8 +28,8 @@
 import com.google.common.eventbus.Subscribe;
 import javax.inject.Inject;
 import lombok.extern.slf4j.Slf4j;
-import net.runelite.api.Actor;
-import net.runelite.api.events.ActorDeath;
+import net.runelite.api.NPC;
+import net.runelite.api.events.NpcDespawned;
 import net.runelite.client.game.ItemManager;
 import net.runelite.client.plugins.Plugin;
 import net.runelite.client.plugins.PluginDescriptor;
@@ -54,9 +54,14 @@ protected void shutDown() throws Exception
 	}
 
 	@Subscribe
-	public void onActorDeath(ActorDeath death)
+	public void onNpcDespawned(NpcDespawned npcDespawned)
 	{
-		Actor actor = death.getActor();
+		NPC actor = npcDespawned.getNpc();
+
+		if (actor.getHealthRatio() != 0)
+		{
+			return;
+		}
 
 		Boss boss = Boss.find(actor.getName());
 		if (boss == null)