Remove unnecessary if statememt in container_manager_linux.go

[mysunshine92]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind cleanup

What this PR does / why we need it:
when --cgroups-per-qos enabled, but --cgroup-root was not specified. kubelet will set --cgroup-root to "/", so this if statement is unnecessary.
Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Hi @mysunshine92. Thanks for your PR.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mysunshine92
To fully approve this pull request, please assign additional approvers.
We suggest the following additional approver: tallclair

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[mysunshine92]

/assign @tallclair

[mattjmcnaughton]

/ok-to-test

Hmm, as the comment says, I'm not sure I'm in favor of removing this. It seems like its useful to have the extra protection against a regression. Although perhaps that regression could be better served with a unit test instead of a runtime check? I guess overall, I'd prefer we either don't remove this or ensure that we add a different check giving us a similar level of protection.

[mattjmcnaughton]

Also, thanks for your pr :)

[k8s-ci-robot]

@mysunshine92: The following tests failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-e2e-gce-100-performance	9ba387e	link	/test pull-kubernetes-e2e-gce-100-performance
pull-kubernetes-kubemark-e2e-gce-big	9ba387e	link	/test pull-kubernetes-kubemark-e2e-gce-big
pull-kubernetes-e2e-gce	9ba387e	link	/test pull-kubernetes-e2e-gce

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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