cubicweb-neuroimaging #3442381 Scan: remove timepoint attribute [open]

Assignment already has a timepoint and Scan always has an Assignment. No need to duplicate.

Remember timepoint is not a datetime but a label such as "baseline", "remission", etc.

prioritynormal
typeenhancement
done in<not specified>
closed by<not specified>
patch[schema] remove timepoint attribute from Scan [applied]