Remove dependency google.golang.org/protobuf/testing/protocmp

[Electronic-Waste]

What you would like to be added?

We will remove a package dependency protocmp from google.golang.org/protobuf/testing/protocmp in unit test files.

Why is this needed?

From Slack:

@Shao Wang Do you think, you have time to remove protocmp from this unit test as well so we can completely remove this dependancy from Katib: https://github.com/kubeflow/katib/blob/d2b0c4852bce239c4655e01520540aaee9e221ad/pk[…]tor/v1beta1/file-metricscollector/file-metricscollector_test.go ?

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[Electronic-Waste]

I will remove it in the following PR.

/assign