Don't duplicate contact information

This could as well fit on tails-project@boum.org

wiki/src/contribute/working_together/code_of_conduct.mdwn

@@ -74,9 +74,3 @@ report it by emailing <tails@boum.org>
 Adapted from the [Django Code of
 Conduct](https://www.djangoproject.com/conduct/), that itself
 attributes it to the [Speak Up! project](http://speakup.io/coc.html).
-
-Questions?
-==========
-
-If you have questions, feel free to contact us:
-<tails@boum.org>.