Removing iframe tag from feed output

Removing iframe tag from feed output

I need to remove an iframe tag that is causing my feed not to work. Here
is the url of the validator VALIDATOR. The url of the feed is Natural
Nigerian Feed. Please could someone tell me what to do. It's been very
frustrating. Here is the code I have written to handle it but it is not
working function rss_noiframe($content) {
// filter out iframe here
$content = preg_replace( '//is', '', $content );
return $content;
}
add_filter('the_excerpt_rss', 'rss_noiframe');
add_filter('the_content_feed', 'rss_noiframe');
add_filter('the_content_rss', 'rss_noiframe'); I put this code inside the
template's function.php but to no avail