Remove etcd2 upgrade/downgrade jobs

[spiffxp]

ref: #7602
ref: kubernetes/enhancements#622
ref: kubernetes/kubernetes#69310

Followup to #9672

As we are no longer supporting etcd2 in v1.13, we no longer need
these jobs

[spiffxp]

/cc @BenTheElder @timothysc

/cc @AishSundar @jberkus
Giving you a heads up as 1.13 release lead and CI signal, this is going to make a sig-release dashboard go away. That said, it's not one we've paid attention to during release cycles

[AishSundar]

thanks @spiffxp for doing this :) Please remove the hold when ready to merge

/lgtm
/hold

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AishSundar, spiffxp

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[spiffxp]

/hold cancel

[k8s-ci-robot]

@spiffxp: Updated the job-config configmap using the following files:

• key sig-cluster-lifecycle-misc.yaml using file config/jobs/kubernetes/sig-cluster-lifecycle/sig-cluster-lifecycle-misc.yaml
• key k8s-upgrade-gce.yaml using file config/jobs/kubernetes/sig-cluster-lifecycle/k8s-upgrade-gce.yaml

In response to this:

ref: #7602
ref: kubernetes/enhancements#622
ref: kubernetes/kubernetes#69310

Followup to #9672

As we are no longer supporting etcd2 in v1.13, we no longer need
these jobs

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