tests/docker: merge debian-native with debian-amd64

tests/docker: merge debian-native with debian-amd64

debian-native isn't really needed and suffers from the problem of
tracking a distros dependencies rather than the projects. With a
little surgery we can make the debian-amd64 container architecture
neutral and allow people to use it to build a native QEMU.

Rename it so it follows the same non-arch pattern of the other distro
containers.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231120150833.2552739-4-alex.bennee@linaro.org>