Revert "Fix cleanup logic for IAM policy bindings (#566)"

[jlewi]

This reverts commit 4ebe571.

The list of service accounts only includes service accounts owned by the
project. So we ended up deleting bindings for service accounts owned by
other projects such as the service accounts.

related to: #566

---

This change is 

[jlewi]

/assign @kunmingg

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Test name	Commit	Details	Rerun command
kubeflow-testing-presubmit	f163829	link	/test kubeflow-testing-presubmit

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[kunmingg]

/lgtm

[jlewi]

Force merging because tests are broken right now because of this.