Refactor signature message checks

[dgrcode]

This check looks unnecessary, as that mismatch would make the signature verification fail. For that to work we should send the currentMessage as first argument in the ethers.utils.verifyMessage call. Sending only data from the client to verify seems like a bad idea to me.

I've tested locally that verification fails if message mismatch and we verify with currentMessage instead of req.body.message.

We can remove this check making the code easier to follow and maintain. I can create an issue to tackle this if you agree with me.

Originally posted by @dgrcode in #31 (comment)

[dgrcode]

Fixed by #48