should pseudata.py should use `fitting_data_dict`?

Created by: scarlehoff

I'm asking because pseudata.py is using common_data_reader https://github.com/NNPDF/nnpdf/blob/74d91831393fff3335397037e498ea7bfd88e492/validphys2/src/validphys/pseudodata.py#L332 which is not what n3fit uses any more.

(@siranipour pinging you since I noticed that while looking at #1285, but it's clearly not part of that PR so didn't want to add entropy there)