Use main-net ENS even when on other networks.

[danfinlay]

The ropsten ENS deployment uses the .test suffix, and so using .ens is a safe way to fetch a recipient address, even when on another network, and so we should allow it.

Inspired by this comment on StackOverflow:
https://ethereum.stackexchange.com/questions/32804/can-metamask-read-ethereum-name-service-ens-addresses/32970?noredirect=1#comment88744_32970

[danfinlay]

@wighawag we have opened an internal issue for tracking this, deleting comment to to prevent reduce spread of possible phishing strategies while we address the issue.

[Gudahtt]

In #7944 we ensured that .eth addresses are only resolved on Mainnet. We could still add support for resolving them on Mainnet while another network is selected globally, but this is already tracked in #6708

I'll close this now, and we can track progress on the remaining work in #6708