refine agent update functions

Author: Jicheng Lu

src/Infrastructure/BotSharp.Core/Repository/FileRepository.cs

@@ -372,13 +372,7 @@ private void UpdateAgentFunctions(string agentId, List<FunctionDef> inputFunctio
         var functionFile = Path.Combine(_dbSettings.FileRepository, _agentSettings.DataDir,
                                         agentId, "functions.json");
 
-        var functions = new List<string>();
-        foreach (var function in inputFunctions)
-        {
-            functions.Add(JsonSerializer.Serialize(function, _options));
-        }
-
-        var functionText = JsonSerializer.Serialize(functions, _options);
+        var functionText = JsonSerializer.Serialize(inputFunctions, _options);
         File.WriteAllText(functionFile, functionText);
     }