Update the Debian instructions for experimental-0.4.1
The 0.4.1 branch is now separate; the 0.3.4 branches are now deprecated.
We should update the website accordingly: https://2019.www.torproject.org/docs/debian.html.en
This change requires the deb.torproject.org change in #30836 (moved), and a successful nightly build of experimental-0.4.1.