In the W3C XML DOM (which is implemented by XML::LibXML, and presumably by XML::DOM), to remove a node, you need to call the removeChild method on its parent node...

use XML::LibXML 2.00;

my $dom    = XML::LibXML->load_xml(IO => \*DATA);
my $answer = $dom->getElementsByTagName('answer')->get_node(1);

$answer->parentNode->removeChild($answer);
print $dom;

__DATA__
<xml>
    <answer>
        <url>http:....</url>
        <content>value 1</content>
    </answer>
    <answer>
        <url>http:....</url>
        <content>value 2</content>
    </answer>
</xml>
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