#!/usr/bin/env perl

use strict;
use warnings;
use Data::Dump;

my %hash = ('a' => ['1', '2'], 'b' => ['2', '3'], 'c' => ['1', '2']);
dd \%hash;
my %seen; 
$seen{join $; => @{$hash{$_}}}++ and delete $hash{$_} for keys %hash;
dd \%hash;

##</code><code>##

{ a => [1, 2], b => [2, 3], c => [1, 2] }
{ a => [1, 2], b => [2, 3] }