xc2par: Partially revert previous cleanup
xc2par: Partially revert previous cleanup

I forgot that despite each individual p-term not having duplicates, a
collection of p-terms can (and probably will) have duplicate inputs

rqou/openfpga,azonenberg/openfpga,azonenberg/openfpga,rqou/openfpga,azonenberg/openfpga,rqou/openfpga,rqou/openfpga,rqou/openfpga,azonenberg/openfpga,azonenberg/openfpga