cgfsng - remove the code checking whether devices cgroup lines are already done

cgfsng - remove the code checking whether devices cgroup lines are already done

We may need to revert this, but I *think* we no longer need this
with default configs.  The idea iirc was that if caller cannot
write to devices.allow (i.e. is in a user namespace), then ignore
permission failures if the cgroups are already sufficiently setup.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>