Enable cgroups-v2 mode on edgeos

This removes cgroups-v2 hybrid mode and enables cgroup2. See also,
https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/22535

BUG=b/221072453
TEST=`mount|grep cgroup2` (`cgroup2 on /sys/fs/cgroup type cgroup2...`)
TEST=cuskyctl (sponge2/d4ff79d4-754c-4fa7-bb84-d050f6baed2f)
RELEASE_NOTE=Enable cgroup v2.

Change-Id: I6db97f6c8f3ae418db5383a8a7daac1b0f07ab45
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/30240
Reviewed-by: Harsh Modi <harshmodi@google.com>
Reviewed-by: Oleksandr Tymoshenko <ovt@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
1 file changed