Adjust note about design proposal archive

Author: rytswd

contributors/design-proposals/README.md

@@ -3,7 +3,3 @@ Design proposals have been archived.
 To view the last version of this document, see the [Design Proposals Archive Repo](https://github.com/kubernetes/design-proposals-archive/).
 
 For information on the replacement design proposal process, see the [Kubernetes Enhancement Proposals (KEP)](https://github.com/kubernetes/enhancements/tree/master/keps/sig-architecture/0000-kep-process) process.
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-Please remove after 2022-04-01 or the release of Kubernetes 1.24, whichever comes first.
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