[Diagnostics] Fix Diagnostics middleware errors (#4271)

Removes setting two forbidden headers.

Author: javiercn

eng/PatchConfig.props

@@ -9,6 +9,7 @@
       Microsoft.AspNetCore.Server.IISIntegration;
       Microsoft.AspNetCore.Server.IntegrationTesting.IIS;
       Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets;
+      Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore;
     </PackagesInPatch>
   </PropertyGroup>
 

src/Middleware/Diagnostics.EntityFrameworkCore/src/README.MD

@@ -0,0 +1,4 @@
+# How to regenerate the error page
+* Go to the Razor Generator project
+* dotnet build
+* run `dotnet .\bin\Debug\netcoreapp2.1\dotnet-razorpagegenerator.dll "Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.Views" "<<PathToAspNetCore>>\src\Middleware\Diagnostics.EntityFrameworkCore\src\"`

src/Middleware/Diagnostics.EntityFrameworkCore/src/Views/DatabaseErrorPage.Designer.cs

@@ -97,8 +97,6 @@
                     var formBody = "context=@JavaScriptEncode(UrlEncode(Model.ContextType.AssemblyQualifiedName))";
                     req.open("POST", "@JavaScriptEncode(Model.Options.MigrationsEndPointPath.Value)", true);
                     req.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
-                    req.setRequestHeader("Content-length", formBody.length);
-                    req.setRequestHeader("Connection", "close");
                     req.send(formBody);
                 }