Release process: drop obsolete info about Debian's RT.

We haven't had access to the relevant RT queues for years
and so far we've survived it, so let's not pretend the RMs
actually check them.

wiki/src/contribute/release_process/Debian_security_updates.mdwn

@@ -8,14 +8,6 @@ by delaying a Tails release a bit to wait for a DSA to happen.
 Debian security team
 ====================
 
-RequestTracker
---------------
-
-The Debian security team uses the [Debian RT](https://rt.debian.org/)
-to track some of their work. Looking at their RT queues might help us
-see if something is being prepared. We, as a Debian derivative, have a
-read-only access to these queues.
-
 Security tracker
 ----------------