fix issue with hiding loading message in embedded mode (#9235)

* fix issue with hiding loading message in embedded mode

* Fix match as well

This chunk of logic only matched on =embed, not =embed=true, which is
what the url given by sharing uses.

src/ui/views/ui_app.jade

@@ -123,9 +123,9 @@ block content
   script.
     window.onload = function () {
 
-      var hideLoadingMessage = /#.*[?&]embed(&|$)/.test(window.location.href);
+      var hideLoadingMessage = /#.*[?&]embed(&|$|=true)/.test(window.location.href);
       if (hideLoadingMessage) {
-        var loading = document.querySelector('.ui-app-loading h1');
+        var loading = document.querySelector('.kibanaWelcomeView');
         loading.removeChild(loading.lastChild);
       }