API docs: Removed stray div.

This fixes the issue with the left sidebar incorectly flowing to
the bottom of the page.

Signed-off-by: Mavridis Philippe <mavridisf@gmail.com>
(cherry picked from commit 131c895e8a)

doc/common/footer.html

@@ -1,4 +1,3 @@
-            </div>
           </div>
         </div>
         <div id="left">

doc/common/mainfooter.html

@@ -11,7 +11,6 @@ Questions about the reference manuals should be sent to
 
 </p>
 </div>
-            </div>
           </div>
         </div>
         <div id="left">