Migrate Rinkeby and Ropsten to use official ENS permanent registrar

[sohkai]

The permanent ENS registrar has been deployed to both Rinkeby and Ropsten, and names can be claimed via https://manager.ens.domains/name/aragonpm.eth

It's a bit of a hassle, but at some point we should redeploy the entire testnet stack such that it's using the real ENS registrar rather than our own.

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This would reset all testnet organization's aragonid names, but we could ask them to ping us to recreate the mapping.