Unused dependency cleanup. (#36760)

* take 2! fight!!!

* final touches

* reeeeeee

Content.Server/Maps/MapMigrationSystem.cs

@@ -1,7 +1,6 @@
 using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
-using Robust.Server.GameObjects;
 using Robust.Shared.ContentPack;
 using Robust.Shared.EntitySerialization.Systems;
 using Robust.Shared.Map.Events;