Remove ONIG_UNICODE_VERSION_... in enc/unicode/case-folding.rb, casefold.h
r55546 defined four macros starting with ONIG_UNICODE_VERSION_...
I haven't found any place where they are used. I don't see any need for them.
If Oniguruma/Onigmo want to introduce them, we can follow, but
we already have RbConfig::CONFIG['UNICODE_VERSION']. If that's not enough, then I suggest we change it so that it's enough in and by itself. As discussed at one of the recent Ruby committers' meetings, there is no plan to let the Unicode Version for Ruby itself and the version for Onigmo to diverge. And Unicode these days is essentially only updated in major versions, so that having four different macros is overkill.
If it turns out that we need these macros in the future, we can always introduce them again, but at the moment, they will just confuse people who are reading the code.