除去っていうよりスクリプトタグ省いたTextが欲しいって事じゃないの?

$doc = new DOMDocument();
$doc->loadHTML(file_get_contents('http://www.nicovideo.jp/'));

$xpathObj = new DOMXPath($doc);
$textNodes = $xpathObj->evaluate('//body//*[name(.)!="script"][normalize-space(child::text()) != ""]/text()');

foreach ($textNodes as $key => $textNode) {
 var_dump($textNode->wholeText);
}