Drop freezer from prow

[psschwei]

We're archiving the container-freezer repo (as discussed in knative-extensions/container-freezer#217), so this PR drops the prow-related config for the freezer.

/assign @dprotaso

[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, psschwei

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[knative-prow]

@psschwei: Updated the job-config configmap in namespace default at cluster default using the following files:

• key container-freezer-main.gen.yaml using file ``
• key container-freezer-release-0.1.gen.yaml using file ``

In response to this:

We're archiving the container-freezer repo (as discussed in knative-extensions/container-freezer#217), so this PR drops the prow-related config for the freezer.

/assign @dprotaso

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