docs: Update download links to point to the first version of ndnSIM.

Change-Id: I5235462cad6f01751bcd5141b2c3e14585d5bed6
diff --git a/docs/Doxyfile b/docs/Doxyfile
index ebe4bb0..d6a2f88 100644
--- a/docs/Doxyfile
+++ b/docs/Doxyfile
@@ -804,7 +804,7 @@
 # the style sheet file to the HTML output directory, so don't put your own
 # stylesheet in the HTML output directory as well, or it will be erased!
 
-HTML_STYLESHEET        = ns3_html_theme/static/ns3_stylesheet.css
+# HTML_STYLESHEET        = ns3_html_theme/static/ns3_stylesheet.css
 
 HTML_EXTRA_FILES       = ns3_html_theme/static/doxygen.css \
                          ns3_html_theme/static/bar-top.png \