Remove old documentation

docs/overrides/404.html

@@ -4,8 +4,7 @@
 {% block content %}
   <h1>404 - Not found</h1>
   <br>
-  FlatBuffers is currently migrating their documentation system and existing 
-  links may not work. 
+  FlatBuffers has migrated their documentation system recently.
   
   Please <a href="https://github.com/google/flatbuffers/issues/new?template=404-doc.md">file an issue</a> indicating the broken link.
 {% endblock %}

docs/overrides/main.html

@@ -1,6 +1 @@
 {% extends "base.html" %}
-
-<!-- Announcement bar -->
-{% block announce %}
-  Documentation migration in progress, view snapshot of the old documentation <a href="https://dbaileychess.github.io/flatbuffers">here.</a>
-{% endblock %}