Delete Cleanup method in e2e util

[gavinfish]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

According to #8309, it seems that the Cleanup method is mainly used in kubectl e2e test cases. And now this method has replaced it.

kubernetes/test/e2e/kubectl/kubectl.go

Lines 166 to 178 in a04c098

	// Stops everything from filePath from namespace ns and checks if everything matching selectors from the given namespace is correctly stopped.
	// Aware of the kubectl example files map.
	func cleanupKubectlInputs(fileContents string, ns string, selectors ...string) {
	ginkgo.By("using delete to clean up resources")
	var nsArg string
	if ns != "" {
	nsArg = fmt.Sprintf("--namespace=%s", ns)
	}
	// support backward compatibility : file paths or raw json - since we are removing file path
	// dependencies from this test.
	framework.RunKubectlOrDieInput(ns, fileContents, "delete", "--grace-period=0", "--force", "-f", "-", nsArg)
	framework.AssertCleanup(ns, selectors...)
	}

Since it is not used across k/k, it is time to delete an used util method.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

none

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

none

[gavinfish]

/assign @oomichi

[tanjunchen]

Good Job.
/lgtm
/assign @alejandrox1

[neolit123]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gavinfish, neolit123

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