Fix wrapped parameters in ultranest

When running the bilby_pipe_review ultranest failed due to the wrapped_params list containing 18 entries, which was more than the number of dimensions that were being searched over. This is because the wrapped_params was set from the prior dictionary that contained both delta function and constraint priors. This MR makes sure the wrapped_params list only gets set from the priors of parameters in the search_parameters_keys, so should be the right length.

It's probably worth checking if this is also required for the pymultinest wrapper, which sets the wrapped_params list in the same way.