Do not hide SPA page while JS is loading

Should improve "visual" loads times, and SEO.

Hiding the page is currently unnecessary
it was added back in 2015 (9c11159), because we used
to rely on the URL path fragment (`#/something`), which
could be different from the page which was currently being loaded.

Author: exyi

src/Framework/Framework/Controls/SpaContentPlaceHolder.cs

@@ -109,12 +109,6 @@ protected internal override void OnPreRender(IDotvvmRequestContext context)
 
         protected override void AddAttributesToRender(IHtmlWriter writer, IDotvvmRequestContext context)
         {
-            if (context.RequestType == DotvvmRequestType.Navigate)
-            {
-                writer.AddStyleAttribute("display", "none");
-            }
-            writer.AddKnockoutDataBind("if", "dotvvm.isSpaReady");
-
             base.AddAttributesToRender(writer, context);
         }