[fix] remove Ubuntu 19.10 from the LXC suite (EOL)

Official support for Ubuntu 19.10 'Eoan Ermine' ended on July 17, 2020.

The image has been dropped [1] from https://images.linuxcontainers.org

[1] https://github.com/lxc/lxc-ci/commit/d161de601bffe4055d77b9d52a826ce5d81567d9



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>