Remove the "tails@boum.org" part of frontdesk

Nowadays, most of the frontdesk people are not on tails@boum.org, so we shouldn’t rely on that anymore. Plus, that work is quite light already, and most not done by them anyway. I propose to simply remove that section.

Feature Branch: doc/8420-tails-boum-frontdesk

Original created by @sajolida on 8420 (Redmine)