Just for kicks here is a perl6 version that uses case...looks much like perl5 so i made it a function.

use v6;

# response to 474872 (remove duplicates regardless of case)

sub remove_dups (@array is copy) {
   my %unique;
   %unique{uc($_)} = 1 for @array;
   return %unique.keys;
}

my @array = ('Hello','hello');
remove_dups(@array).say;
@array.say;
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