Revert "Change nonconjugate class to keep a running logp score"

[ThomasColthurst]

This reverts commit fc9115366521570c714322746df351b9cebac4d1.

I remembered why it is important to memorize the data and have logp_score compute the log probabilities -- it is because the latent variables can change after the data has been incorporated.

[emilyfertig]

Aha good point.