remove ethical ads markup (it pushes the survey nav down too far)

Author: goatlady

docs/_templates/survey/header.html

@@ -1,5 +1,4 @@
 <a href="https://www.writethedocs.org/"><img src="/_static/sticker-wtd-colors.png" alt="Write the Docs logo"></a>
 {% include 'info.html' %}
 <a href="/">Back to main site</a>
-<br>
-<div id="ethical-ad-placement"></div>
+<br>