Remove redundant import.

[numerology]

Remove some redundant imports from a notebook.

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This change is 

[k8s-ci-robot]

Hi @numerology. Thanks for your PR.

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[numerology]

/assign @gaoning777

[Ark-kun]

/ok-to-test

[gaoning777]

/test kubeflow-pipeline-sample-test

[gaoning777]

/lgtm

[gaoning777]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gaoning777

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