Tutorial on n3fit pseudodata is outdated

Created by: Zaharid

This tutorial

https://docs.nnpdf.science/tutorials/pseudodata.html?highlight=pseudodata

seems outdated. Foe one we don't have a get_pseudodata action

 $ validphys --help get_pseudodata
No help available for get_pseudodata
Instead of 'get_pseudodata', did you mean one of the following?
 - training_pseudodata
 - recreate_pdf_pseudodata
 - recreate_fit_pseudodata