MON-3801: clean-up unused OAuth proxy references

[simonpasquier]

After the 4.16-release branch being cut, we have code related to OAuth proxy that can be removed now.

• [ ] I added CHANGELOG entry for this change.
• [x] No user facing changes, so no entry in CHANGELOG was needed.

[openshift-ci-robot]

@simonpasquier: This pull request references MON-3801 which is a valid jira issue.

Warning: The referenced jira issue has an invalid target version for the target branch this PR targets: expected the task to target the "4.17.0" version, but no target version was set.

In response to [this](https://github.com/openshift/cluster-monitoring-operator/pull/2359): >After the 4.16-release branch being cut, we have code related to OAuth proxy that can be removed now. > > > >* [ ] I added CHANGELOG entry for this change. >* [ ] No user facing changes, so no entry in CHANGELOG was needed. > Instructions for interacting with me using PR comments are available [here](https://prow.ci.openshift.org/command-help?repo=openshift%2Fcluster-monitoring-operator). If you have questions or suggestions related to my behavior, please file an issue against the [openshift-eng/jira-lifecycle-plugin](https://github.com/openshift-eng/jira-lifecycle-plugin/issues/new) repository.

[simonpasquier]

/skip

[simonpasquier]

/retest-required

[openshift-ci[bot]]

@simonpasquier: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/versions	a908e429e15b475bc5b1aec4211b577023a4eebe	link	false	/test versions

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository. I understand the commands that are listed [here](https://go.k8s.io/bot-commands).

[machine424]

/lgtm thanks

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: machine424, simonpasquier

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