Removes xps fitting region in example

While testing in nomad I've seen that the fitting with the provided fit region is off. Therefore, I removed the fit_region entirely which produces a nicer fit.

@rumo Please check the fit quality and approve if you agree. Feel free to merge this if you are happy with this change. Also is there a reason why this changed? Did you change the reading of axis and do we expect a shift here?

requested review from @rumo

changed the description

This is looks fine. I also showed something like this in fairmat coffee presentation. Probably, in the mean time working on xps error something is changed.

mentioned in commit 4bdb9367

merged