[Perl/perl5] 29e2ba: locale.c: Remove PERL_UNUSED_ARG

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 29e2ba2cb5cd3460670ec96da9cd580ab6bb07b5
      
https://github.com/Perl/perl5/commit/29e2ba2cb5cd3460670ec96da9cd580ab6bb07b5
  Author: Karl Williamson <k...@cpan.org>
  Date:   2024-01-04 (Thu, 04 Jan 2024)

  Changed paths:
    M locale.c

  Log Message:
  -----------
  locale.c: Remove PERL_UNUSED_ARG

'which_mask' is now always used