Remove ethereumjs-util dependency

[tyleryasaka]

We're using ethereumjs-util to do signature validation. We should be able to do all this in web3 and remove this dependency.

[nick]

Although this is possible with web3, it does not happen in the client and instead goes back to the node and, unfortunately, the personal_ecRecover method isn't supported everywhere (including Infura which is used by MetaMask).

Agree it'd be nice to remove the ethereumjs-util dependency though.

[tyleryasaka]

Ok, probably not worth it right now then. Closing.