Remove EIP155 workaround (Signer)

[axelchalon]

Now that ethereumjs/ethereumjs-tx#143 is merged, we should be able to remove this workaround https://github.com/paritytech/fether/blob/95452ee350dd9d90717a6d630b58013b4caaa040/packages/fether-react/src/utils/transaction.js#L165-L188 (used for signing transactions with Parity Signer) and simply use the methods from the library instead.