Removing deprecated parameter (#12004) (#12007)

Fixes: https://github.com/vaadin/framework/issues/11958

Authored-by: Tatu Lund <tatu@vaadin.com>

server/src/main/java/com/vaadin/server/BootstrapHandler.java

 
         Document document = response.getDocument();
 
-        DocumentType doctype = new DocumentType("html", "", "",
-                document.baseUri());
+        DocumentType doctype = new DocumentType("html", "", "");
         document.child(0).before(doctype);
 
         Element head = document.head();