Make DerivingVia a package default.

[fisx]

This has been bugging me for a while. I'll just add this minimal commit so we won't have to mention DerivingVia in the package heades any more in the future, but I'll leave the old ones in there for the sake of laziness.

[pcapriotti]

Yes, good idea. It would be nice to remove the corresponding pragmas as well. This should do it:

fd -ehs --exec sed -i '/LANGUAGE DerivingVia/d'

[fisx]

fd looks cool, thanks for the pointer! (package fd-find in debian)

(for the record: i deliberately decided against removing it to make this as simple and swift as possible and then move back to other business. but entering one more command wasn't too bad either. :))

[pcapriotti]

Looks good!