cgroupv2/systemd: privatize UnifiedManager
cgroupv2/systemd: privatize UnifiedManager

... and its Cgroup field. There is no sense to keep it public.

This was generated by gorename.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

rhatdan/runc,estesp/runc,kolyshkin/runc,mikebrow/runc,dqminh/runc,mikebrow/runc,estesp/runc,rhatdan/runc,kolyshkin/runc,kolyshkin/runc,opencontainers/runc,kolyshkin/runc,dqminh/runc,rhatdan/runc,xiaochenshen/runc,xiaochenshen/runc,dqminh/runc,xiaochenshen/runc,opencontainers/runc,opencontainers/runc,mikebrow/runc,dqminh/runc,opencontainers/runc,estesp/runc,rhatdan/runc