Fix #135 & #161 & #140 (#162)

## Purpose
<!-- Describe the intention of the changes being proposed. What problem
does it solve or functionality does it add? -->
Clean services that used by /ask

Related issue:
- #135 
- #161 
- #140 
This PR also remove `ApproachServiceResponseFactory` and GPT model that
used for text completion

## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[ ] No
```

## Pull Request Type
What kind of change does this Pull Request introduce?

<!-- Please check the one that applies to this PR using "x". -->
```
[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:
```

## How to Test
*  Get the code

```
git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install
```

* Test the code
<!-- Add steps to run the tests suite and/or manually test -->
```
```

## What to Check
Verify that the following are valid
* ...

## Other Information
<!-- Add any other helpful information that may be needed here. -->

app/backend/Extensions/ServiceCollectionExtensions.cs

@@ -65,32 +65,11 @@ internal static IServiceCollection AddAzureServices(this IServiceCollection serv
             return openAIClient;
         });
 
-        services.AddSingleton<IKernel>(sp =>
-        {
-            // Semantic Kernel doesn't support Azure AAD credential for now
-            // so we implement our own text completion backend
-            var config = sp.GetRequiredService<IConfiguration>();
-            var azureOpenAiGptDeployment = config["AzureOpenAiGptDeployment"];
-
-            var openAITextService = sp.GetRequiredService<AzureOpenAITextCompletionService>();
-            var kernel = Kernel.Builder.Build();
-            kernel.Config.AddTextCompletionService(azureOpenAiGptDeployment!, _ => openAITextService);
-
-            return kernel;
-        });
-
         services.AddSingleton<AzureBlobStorageService>();
 
-        services.AddSingleton<AzureOpenAITextCompletionService>();
         services.AddSingleton<AzureOpenAIChatCompletionService>();
         services.AddSingleton<ReadRetrieveReadChatService>();
 
-        services.AddSingleton<IApproachBasedService, RetrieveThenReadApproachService>();
-        services.AddSingleton<IApproachBasedService, ReadRetrieveReadApproachService>();
-        services.AddSingleton<IApproachBasedService, ReadDecomposeAskApproachService>();
-
-        services.AddSingleton<ApproachServiceResponseFactory>();
-
         return services;
     }
 

app/backend/GlobalUsings.cs

@@ -13,7 +13,6 @@
 global using Azure.Storage.Blobs.Models;
 global using Microsoft.AspNetCore.Mvc;
 global using Microsoft.AspNetCore.Mvc.RazorPages;
-global using Microsoft.Extensions.Caching.Distributed;
 global using Microsoft.ML;
 global using Microsoft.ML.Transforms.Text;
 global using Microsoft.SemanticKernel;
@@ -22,10 +21,8 @@
 global using Microsoft.SemanticKernel.AI.TextCompletion;
 global using Microsoft.SemanticKernel.Memory;
 global using Microsoft.SemanticKernel.Orchestration;
-global using Microsoft.SemanticKernel.SkillDefinition;
 global using MinimalApi.Extensions;
 global using MinimalApi.Services;
-global using MinimalApi.Services.Skills;
 global using PdfSharpCore.Pdf;
 global using PdfSharpCore.Pdf.IO;
 global using Shared;

app/backend/Services/AzureOpenAIChatCompletionService.cs

@@ -37,8 +37,8 @@ public async Task<string> CompleteAsync(
         var response =
             await _openAIClient.GetCompletionsAsync(
                 _deployedModelName, option, cancellationToken);
-        return response.Value is Completions completions && completions.Choices.Count > 0
-            ? completions.Choices[0].Text
+        return response.Value is Completions completions && completions.Choices.Count > 0
+            ? completions.Choices[0].Text
             : throw new AIException(AIException.ErrorCodes.InvalidConfiguration, "completion not found");
     }
 }