Removed prior_penalty in dsge_likelihood.

If options_.prior_trunc is set to zero (the default is strictly positive) then prior_correction is infinite because the prior density is zero (this is not true for the uniform prior)... This does not help the optimizer. Even if we do not fall in this case (because options_.prior_trunc>0 or becuase only uniform priors are used for the bounded parameters) the meaning of this correction is unclear.