use XML::LibXML 1.93;
use XML::LibXML::PrettyPrint qw/print_xml/;

my $doc = XML::LibXML->load_xml(IO => \*DATA);

$doc
	-> findnodes('//policyrules')
	-> foreach(sub {
			my $elem = shift;
			$elem->parentNode->appendChild($_) foreach $elem->childNodes;
			$elem->parentNode->removeChild($elem);
	   });

print_xml($doc);

__DATA__
<?xml version="1.0" encoding="UTF-8"?>
<policy name="Cur_policy" version="3.2.1">
  <policyrules>
    <Rule Action="allow" Enabled="true" RuleID="F68E32">
      <source addr="10.4.5.3" srcport="any"/>
      <dest addr="199.5.4.3" destport="80"/>
    </Rule>
    <Rule Action="allow" Enabled="true" RuleID="78E21D">
      <source addr="10.4.0.0-10.4.255.255" srcport="any"/>
      <dest addr="any" destport="80"/>
    </Rule>
  </policyrules>
</policy>