cgroupv1/systemd.Set: don't enable kernel memory acct
cgroupv1/systemd.Set: don't enable kernel memory acct

This is a regression from commit 1d4ccc8e0. We only need to enable
kernel memory accounting once, from the (*legacyManager*).Apply(),
and there is no need to do it in (*legacyManager*).Set().

While at it, rename the method to better reflect what it's doing.

This saves 1 call to mountinfo parser.

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

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