Refactor mind and ghost deletion code (#3680)

* Refactor mind and ghost deletion code

* Refactor to use EventBus and clean up deletes

* Fix mind eject when being deleted

* Refactor entity manager calls to use IEntity.EntityManager

Content.Server/GameObjects/EntitySystems/GhostSystem.cs

@@ -0,0 +1,44 @@
+#nullable enable
+using Content.Server.GameObjects.Components.Mobs;
+using Content.Server.GameObjects.Components.Observer;
+using JetBrains.Annotations;
+using Robust.Server.GameObjects;
+using Robust.Shared.GameObjects;
+using System;
+
+namespace Content.Server.GameObjects.EntitySystems
+{
+    [UsedImplicitly]
+    public class GhostSystem : EntitySystem
+    {
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<GhostComponent, MindRemovedMessage>(OnMindRemovedMessage);
+            SubscribeLocalEvent<GhostComponent, MindUnvisitedMessage>(OnMindUnvisitedMessage);
+        }
+
+        private void OnMindRemovedMessage(EntityUid uid, GhostComponent component, MindRemovedMessage args)
+        {
+            if (!EntityManager.TryGetEntity(uid, out var entity))
+                return;
+            DeleteEntity(entity);
+        }
+
+        private void OnMindUnvisitedMessage(EntityUid uid, GhostComponent component, MindUnvisitedMessage args)
+        {
+            if (!EntityManager.TryGetEntity(uid, out var entity))
+                return;
+            DeleteEntity(entity);
+        }
+
+        private void DeleteEntity(IEntity? entity)
+        {
+            if (entity?.Deleted == true)
+                return;
+
+            entity?.Delete();
+        }
+    }
+}