Remove obsolete Azure ForwardedHeaders workaround. (#359)

Author: Tratcher

src/Microsoft.AspNetCore.Server.IISIntegration/WebHostBuilderIISExtensions.cs

@@ -57,13 +57,6 @@ public static IWebHostBuilder UseIISIntegration(this IWebHostBuilder hostBuilder
                     services.Configure<ForwardedHeadersOptions>(options =>
                     {
                         options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;
-
-                        // https://github.com/aspnet/IISIntegration/issues/140
-                        // Azure Web Sites needs to be treated specially as we get an imbalanced set of X-Forwarded-* headers.
-                        // We use the existence of the %WEBSITE_INSTANCE_ID% environment variable to determine if we're running
-                        // in this environment, and if so we disable the symmetry check.
-                        var isAzure = !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("WEBSITE_INSTANCE_ID"));
-                        options.RequireHeaderSymmetry = !isAzure;
                     });
                 });
             }