libct/cg/fs2.Stat: don't look for available controllers
libct/cg/fs2.Stat: don't look for available controllers

Some controllers might still have stats available even if they are
disabled (this is definitely so for cpu.stat -- see earlier commit).

Some stat methods might implement sensible fallbacks (see previous
commit for statPids.

In the view of all that, it makes sense to not check if a particular
controller is available, but rather ignore ENOENT from it.

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

rhatdan/runc,kolyshkin/runc,rhatdan/runc,dqminh/runc,opencontainers/runc,opencontainers/runc,kolyshkin/runc,opencontainers/runc,kolyshkin/runc,dqminh/runc,opencontainers/runc,dqminh/runc,rhatdan/runc,rhatdan/runc,kolyshkin/runc,dqminh/runc