Removed unused using statements

src/Server/AIProvider.cs

@@ -1,9 +1,5 @@
 
-using System.Collections.Frozen;
-using System.Collections.Immutable;
 using System.Text;
-using System.Text.Json;
-using System.Text.Json.Serialization;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 using Server.Exceptions;