remove not used IsStaticPod, prevent possible panic

[gy95]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

1. function IsStaticPod is never used

   kubernetes/pkg/kubelet/pod/mirror_client.go

   Lines 156 to 160 in 513ae55

   	// IsStaticPod returns true if the passed Pod is static.
   	func IsStaticPod(pod *v1.Pod) bool {
   	source, err := kubetypes.GetPodSource(pod)
   	return err == nil && source != kubetypes.ApiserverSource
   	}

   
   And there is the same function in

   kubernetes/pkg/kubelet/types/pod_update.go

   Lines 149 to 153 in 513ae55

   	// IsStaticPod returns true if the pod is a static pod.
   	func IsStaticPod(pod *v1.Pod) bool {
   	source, err := GetPodSource(pod)
   	return err == nil && source != ApiserverSource
   	}

So we can remove the first definition

2. function func IsMirrorPod(pod *v1.Pod) bool doesn't check whether Annotations is nil or not.
   but in the function above IsStaticPod, it calls GetPodSource, and this function check whether Annotations is nil or not

kubernetes/pkg/kubelet/types/pod_update.go

Lines 104 to 111 in 513ae55

	func GetPodSource(pod *v1.Pod) (string, error) {
	if pod.Annotations != nil {
	if source, ok := pod.Annotations[ConfigSourceAnnotationKey]; ok {
	return source, nil
	}
	}
	return "", fmt.Errorf("cannot get source of pod %q", pod.UID)
	}

i think we can check also, but i'm not very sure it is need to check.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

Hi @gy95. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[pacoxu]

/release-note-none
LGTM

[ehashman]

/ok-to-test
/priority backlog
/triage accepted
/lgtm

Assuming tests pass, I agree this is unused in favour of

kubernetes/pkg/kubelet/types/pod_update.go

Lines 149 to 153 in 671251a

	// IsStaticPod returns true if the pod is a static pod.
	func IsStaticPod(pod *v1.Pod) bool {
	source, err := GetPodSource(pod)
	return err == nil && source != ApiserverSource
	}

See https://cs.k8s.io/?q=IsStaticPod&i=nope&files=&excludeFiles=&repos=kubernetes/kubernetes

[gy95]

/test pull-kubernetes-e2e-gce-100-performance

[gy95]

ping

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gy95, mrunalp

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