Remove unnecessary checks

[free2k]

Graceful shutdown and kill with SIGRTMIN..SIGRTMAX don't work.

moby/moby#36219
opencontainers/runc#1706

I found this problem in the actual scene, I hope to fix this bug.

[unshare]

Clean cherry-pick is possible.
@free2k: Have you reported it in RHBZ? If you have a RHEL subscription, it'll be even more great.

[free2k]

@unshare I have already submitted this question to RHBZ