libutils: do not follow process's group

1) App doesn't have cgroup access and there is no purpose of reading cgroup
for app. For system_server it should be known in foreground group. So
there is no benefit of reading group.

2) Reading cgroup in apps can also cause contention for other cgroup
operations.

3) vendor can change cgroup setting and get_sched_policy may return
incorrect information for get_sched_policy_profile_name.

Test: Boot
Bug: 210011562
Signed-off-by: Wei Wang <wvw@google.com>
Change-Id: I8e8c8b346984781c56ec93c0616121f7d5c99fe5