.Net: OpenAI V2 - Small fix (#8015)

## Small fix

- Remove remaining comments.

dotnet/src/Connectors/Connectors.OpenAI/Core/ClientCore.cs

@@ -1,20 +1,5 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-/* 
-Phase 01 : This class was created adapting and merging ClientCore and OpenAIClientCore classes.
-System.ClientModel changes were added and adapted to the code as this package is now used as a dependency over OpenAI package.
-All logic from original ClientCore and OpenAIClientCore were preserved.
-
-Phase 02 :
-- Moved AddAttributes usage to the constructor, avoiding the need verify and adding it in the services.
-- Added ModelId attribute to the OpenAIClient constructor.
-- Added WhiteSpace instead of empty string for ApiKey to avoid exception from OpenAI Client on custom endpoints added an issue in OpenAI SDK repo. https://github.com/openai/openai-dotnet/issues/90
-
-Phase 05:
-- Model Id became not be required to support services like: File Service.
-        
-*/
-
 using System;
 using System.ClientModel;
 using System.ClientModel.Primitives;