Outdated nullified attributes

I'm going to delete these. They're probably some TC211 leftovers, not very useful here nor in any future project.

https://github.com/glossarist/iev-data/blob/b07e79e07f1502d7fea75cf62fdbdcf88fcf1246/lib/iev/termbase/term_builder.rb#L72-L85

They are further "used" in https://github.com/glossarist/iev-data/blob/master/lib/iev/termbase/term.rb.

@ronaldtse WDYT?

Start with the linked lines 72-85 in lib/iev/termbase/term_builder.rb, then inspect the corresponding uses in lib/iev/termbase/term.rb. Confirm which attributes are the outdated TC211 leftovers and check their references before removing them; done means the obsolete attributes and their uses are gone without leaving broken references.

Written by the indexing model from the issue text.