#!/usr/bin/perl

use strict;
use warnings;

use XML::Twig;

my $twig_to_del=XML::Twig->new(
                        twig_handlers=>{
                                        #to_delete elements
                                        '/document/header'=> sub { $_->delete if $_->prev_sibling( 'header'); },
                                        },
                        )
                         ->parse(\*DATA)
                         ->print;


__DATA__
<document>
  <header>h1</header>
  <header>h2</header>
  <header>h3</header>
</document>