Remove section on debian packages for now

The last packaged version is now not supported anymore. So this is to
make sure we don't advertise to new people and confuse them later.

website/download.shtml

@@ -45,26 +45,6 @@ See the <a href="https://hub.docker.com/r/domjudge/domserver/">Docker Hub
 repository for the DOMserver</a> to get started.
 </p>
 
-<h3>Debian Packages</h3>
-
-<p>There are <a href="https://www.debian.org">Debian</a> packages
-available for the amd64 architecture; other architectures might be buildable
-from the source packages.
-The packages are built and tested on Debian <em>stable</em>, but also on newer versions and the various versions of Ubuntu.</p>
-
-<p>To install these packages, add our
-<a href="/repokey.asc">repository GPG key</a> directly to APT with</p>
-<pre>curl -o - https://www.domjudge.org/repokey.asc | sudo tee /etc/apt/trusted.gpg.d/domjudge.org.asc</pre>
-<p>or first check our signatures on the key for authenticity.
-Then add the following lines to <code>/etc/apt/sources.list</code>:</p>
-<pre>
-deb     https://domjudge.org/debian unstable/
-deb-src https://domjudge.org/debian unstable/
-</pre>
-<p>Note the slash following <code>unstable</code> and the missing
-section(s) <code>main contrib non-free</code>.
-</p>
-
 <h3>Other downloads</h3>
 
 <p>The <a href="/snapshot/">snapshot directory</a> contains nightly builds,