Truncating NaNs and Infs

[gflegar]

@antodo was doing some changes to the paper - trying to explain why we truncate NaNs and Inf, and figured out we do not actually need to do it.
Since we are already storing the data to the backed type, an not in lower precision, we can just store whatever was there before (it's still a NaN or Info).

Basically, we should be able to just delete the following line: https://github.com/oprecomp/FloatX/blob/master/src/floatx.hpp#L1015