Simplify cgroups.json

cgroups.json causes the following changes to be applied twice to
/sys/fs/cgroup: change user ID to system, change group ID to system and
change mode to 0755. Apply these settings once instead of twice.

Bug: 213617178
Test: Ran ls -ld /sys/fs/cgroup in Cuttlefish.
Change-Id: Ieb953c186c027b989599cbbaa70a9c9324678cdf
Signed-off-by: Bart Van Assche <bvanassche@google.com>