`url` crate used by `tendermint` does not support no_std

[soareschen]

The struct url::Url is used inside tendermint::net, however the url crate cannot work under no_std. We would have to either move tendermint::net to a separate crate, or find an alternative crate that supports no_std.

Note that the tendermint::net module is not used in any part of the ibc crate. However it is not clear whether it is used indirectly by ibc elsewhere, which would complicate the issue.

There is a recent pending PR in August 2021 to support no_std in url: servo/rust-url#717. However it is not clear when it will get merged. An alternative solution would be to contribute upstream and push for that PR to get merged and released soon.

[seanchen1991]

Does #986 address the url crate's no_std compliance in any way?

[soareschen]

Does #986 address the url crate's no_std compliance in any way?

tendermint-config do not have to be no_std-compliant. Only tendermint crate needs to be, and in this PR we have removed the url dependency in tendermint crate itself.

[soareschen]

This has been addressed with the use of Url moved to tendermint-config.