<!-- Generator: Adobe Illustrator 17.1.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->

<g id="svgSteps">
</g>
<g id="svgBase">
</g>

$fileContent = file_get_contents('my_file');
$fileContent = preg_replace('/<!--(.|s)*?-->/','',$fileContent);
file_put_contents('my_file',$fileContent);

preg_replace("/((<g id=".*">)|(<g>))[s]*(</g>)/",'',$fileContent)
    preg_replace("/(<!--)[sS]*(-->)/",'',$fileContent)

$fileContent = preg_replace('#<!--.*?-->#s', '', $fileContent);
$fileContent = preg_replace('#<(w+)(?:s+[^>]+)?>s*</1>#s', '', $fileContent);

<?php
$fileContent = '<!-- Generator: Adobe Illustrator 17.1.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  --> asdlfhjlkasdjhfasdf asd <g id="kjkjkh" /> askdjghf ag <g id="eeee" > </g>ahsdjghakjhglkjdahlg';
$fileContent = preg_replace('/(<!--(.|s)*-->)?([nwW]*)?/','$3',$fileContent);
$fileContent = preg_replace('/<[gG]?s+[Ii][Dd]="?w+"s*(?:/>|>)[st]*(</[gG]>)?/', ' ',$fileContent);
echo($fileContent);
?>