Remove unused AuthExtensions.cs and its extension method

Deleted the AuthExtensions.cs file, which included the AuthorizePolicyAsync extension for IAuthorizationService. This method and related code were no longer needed.

EnvelopeGenerator.API/Extensions/AuthExtensions.cs

@@ -1,25 +0,0 @@
-using Microsoft.AspNetCore.Authorization;
-using System.Security.Claims;
-
-namespace EnvelopeGenerator.API.Extensions;
-
-/// <summary>
-/// 
-/// </summary>
-public static class AuthExtensions
-{
-    /// <summary>
-    /// 
-    /// </summary>
-    /// <param name="authService"></param>
-    /// <param name="user"></param>
-    /// <param name="policyName"></param>
-    /// <returns></returns>
-    public static async Task<bool> AuthorizePolicyAsync(this IAuthorizationService authService,
-                                                  ClaimsPrincipal user,
-                                                  string policyName)
-    {
-        var result = await authService.AuthorizeAsync(user, policyName);
-        return result.Succeeded;
-    }
-}