Refactor .Net example project (#1049)

Co-authored-by: 东风破 <birdfishs@163.com>

scripts/dotnet/OfflineModelConfig.cs

@@ -1,13 +1,10 @@
 /// Copyright (c)  2024.5 by 东风破
 
-using System.Linq;
-using System.Collections.Generic;
 using System.Runtime.InteropServices;
-using System.Text;
-using System;
 
 namespace SherpaOnnx
 {
+
     [StructLayout(LayoutKind.Sequential)]
     public struct OfflineModelConfig
     {
@@ -55,4 +52,6 @@ namespace SherpaOnnx
         [MarshalAs(UnmanagedType.LPStr)]
         public string TeleSpeechCtc;
     }
-}
+
+
+}