UnicodeNormalize::UNICODE_VERSION is defined in lib/unicode_normalize/tables.rb, but we now also have RbConfig::CONFIG['UNICODE_VERSION'], which is more general. Therefore, UnicodeNormalize::UNICODE_VERSION can be removed.
I'm opening an issue on this just in case somebody is depending on this. I have searched all of Ruby proper (incl. standard libraries) and removed any uses that I found.
I'll implement this feature if I don't get some pushback in a week or so.
lib/unicode_normalize/tables.rb is automatically generated from template/unicode_norm_gen.tmpl.
You have to change not only the former but also the latter.