Remove usage of obsolete with_subnavigation parameter

The layouts/header partial doesn't use this parameter since commit
488e7e081, where it was deleted while solving a merge conflict.

app/views/layouts/application.html.erb

@@ -18,7 +18,7 @@
     <%= raw setting["html.per_page_code_body"] %>
 
     <div class="wrapper <%= yield(:wrapper_class) %>">
-      <%= render "layouts/header", with_subnavigation: true %>
+      <%= render "layouts/header" %>
 
       <main id="main" class="public-content <%= yield(:main_class) %>">
         <%= render "layouts/flash" %>

app/views/layouts/dashboard.html.erb

@@ -18,7 +18,7 @@
 
     <h1 class="show-for-sr"><%= setting["org_name"] %></h1>
 
-    <%= render "layouts/header", with_subnavigation: false %>
+    <%= render "layouts/header" %>
 
     <div class="menu-and-content">
       <%= check_box_tag :show_menu, nil, false, role: "switch" %>