Disable sampling of transformed variables from `prior_predictive`

[ricardoV94]

This was added to facilitate sampling from the prior as a starting point for SMC, but with the new functions added in #4983 this is no longer needed.

https://github.com/pymc-devs/pymc/blob/6d2aa5ddebed01d81c2ab66b9d4bd02194f82508/pymc3/sampling.py#L1983-L1999

[markvrma]

I'd like to take up this issue.

[purna135]

Is it okay if I work on this?

[ricardoV94]

Is it okay if I work on this?

Sure

[purna135]

I need some assistance in replacing the following code with make_initial_point_fn https://github.com/pymc-devs/pymc/blob/e6fc2ec100dafacca4f0b9eab40661174707afcd/pymc/smc/smc.py#L179-L184

https://github.com/pymc-devs/pymc/blob/d84c71884762fb925eb7272b9d28e879399e326a/pymc/initial_point.py#L130

[ricardoV94]

You will have to change the parameters of make_initial_point_fn so that it is returning draws from the transformed prior. You can do that by setting the overrides dictionary so that every value variable strategy is "prior", and also switching the default from "moment" to "prior". Then you will need to make sure you call the returned function with a different seed self.draws times.