Spdz output to single protocol does not covert representation

There is an inconsistency between the regular spdz output to all protocol and the spdz output to single party protocol: output to all converts the representation of the value to its signed version, output to single does not.

Non of the protocols should do the conversion. It should be up to the user whether they want to convert.

The main difficulty here is to adjust tests to expect non-converted outputs.