MEG - Remove unused fields in subject_info.json

[allermat]

There are fields in the subject_info.json file which aren't explicitly used by the code such as, meg_id, meg_date, mri_id and mri_date. This is because all those are also included in the corresponding file paths which are actually used in the code.

I thought it is nice to have those fields as when you look at the subject_info.json file you can immediately identify which subject is which based on those fields, but I acknowledge that those fields aren't strictly necessary.

Shall we keep or get rid of them?

Let me know what you think @RikHenson, @dcdace, @olafhauk

Thanks!

[RikHenson]

I would remove unused fields, to also reduce problem of PID, though I guess people will share BIDS repositories but not necessarily the scripts that produce the BIDS...

[allermat]

I guess people will share BIDS repositories but not necessarily the scripts that produce the BIDS...

Indeed, the subject_info.json is not for sharing.