kvm-tools: remove make_root_dir()

The root dir was already created by kvm__set_dir() which is in main().

Acked-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>