docker: remove unused debian8 partial image

debian8 partial base is also not consumed by any image, so remove it.
For QEMU's development cycle, we only support debian9 (stretch) and
debian10 (buster).

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190923181140.7235-3-jsnow@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
2 files changed