Drop custom image registry config manifest

[russellb]

This issue is to track the removal of:

https://github.com/openshift-metal3/dev-scripts/blob/master/assets/templates/99_registry.yaml

It can be removed when the following PR is merged:

openshift/cluster-image-registry-operator#332

[dhellmann]

@russellb I see #623 refers to this. Does that resolve this issue, or is there still work to do?

[russellb]

There's still work to do. 99_registry.yaml is still there. It's pending outcome of openshift/cluster-image-registry-operator#332

[russellb]

openshift/cluster-image-registry-operator#332 has merged so we can remove the registry manifest once that shows up in a nightly release