Removed workaround for dotnet/aspnetcore#32097

Author: Bart Koelman

src/JsonApiDotNetCore/Middleware/JsonApiMiddleware.cs

@@ -11,7 +11,6 @@
 using JsonApiDotNetCore.Serialization.Objects;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Extensions;
-using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Mvc.Controllers;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.Logging;
@@ -130,8 +129,6 @@ private static async Task<bool> ValidateContentTypeHeaderAsync(string allowedCon
         {
             string? contentType = httpContext.Request.ContentType;
 
-            // ReSharper disable once ConditionIsAlwaysTrueOrFalse
-            // Justification: Workaround for https://github.com/dotnet/aspnetcore/issues/32097 (fixed in .NET 6)
             if (contentType != null && contentType != allowedContentType)
             {
                 await FlushResponseAsync(httpContext.Response, serializerOptions, new ErrorObject(HttpStatusCode.UnsupportedMediaType)