shadown_%.bbapend: hardening of password settings

Remove the hardening distro requirement from the recipe,
we do not want to rename our distro and this feature is useful
in all cases.

One thing that needs to be added is setting up the password min/max
age, and the minimum password length.

Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>