themes: use noscript for search js notification

The "search.html" template will generate a warning admonition about
requiring JavaScript for search and automatically hiding the element
when supported. While functional, if a client renders the page slowly,
the warning notification may be visible to the user for a moment.

Instead of relying on JavaScript to suppress this warning, use a
`noscript` tag to hide the warning for clients who do not support
JavaScript. This also has the benefit of one less JavaScript call
required by a client.

Signed-off-by: James Knight <james.d.knight@live.com>

sphinx/themes/basic/search.html

@@ -21,13 +21,14 @@
 {% block body %}
   <h1 id="search-documentation">{{ _('Search') }}</h1>
   {% block scriptwarning %}
-  <div id="fallback" class="admonition warning">
-  <script>$('#fallback').hide();</script>
+  <noscript>
+  <div class="admonition warning">
   <p>
     {% trans %}Please activate JavaScript to enable the search
     functionality.{% endtrans %}
   </p>
   </div>
+  </noscript>
   {% endblock %}
   {% block searchtext %}
   <p>