Remove legacy migration

ChatTwo/Code/ChatCode.cs

@@ -1,6 +1,3 @@
-using Dalamud.Game.Config;
-using LiteDB;
-
 namespace ChatTwo.Code;
 
 internal class ChatCode
@@ -22,15 +19,6 @@ internal class ChatCode
         Target = SourceFrom(7);
     }
 
-    [BsonCtor] // Used by LegacyMessageImporter
-    public ChatCode(ushort raw, ChatType type, ChatSource source, ChatSource target)
-    {
-        Raw = raw;
-        Type = type;
-        Source = source;
-        Target = target;
-    }
-
     internal ChatType Parent() => Type switch
     {
         ChatType.Say => ChatType.Say,