Header image not showing on posts

I wanted to hide the featured image on my posts so I added the following to my index.php file. However, now it is also hiding the header image at the top of the page (it used to show the same one as on the homepage here: https://www.birdzofafeather.ca). Is there a way to get the header back, but still hide the featured image?

function wordpress_hide_feature_image( $html, $post_id, $post_image_id ) {
return is_single() ? ” : $html;
}
// add the filter
add_filter( ‘post_thumbnail_html’, ‘wordpress_hide_feature_image’, 10, 3);

The page I need help with: [log in to see the link]