Remove featured image if it appears in "the_content" WordPress filter

filter.php

```php<?php
add_filter( 'the_content', function ($content) {
    $content = mb_convert_encoding($content, 'HTML-ENTITIES', "UTF-8");
    $featured_image = get_the_post_thumbnail_url($post->ID);

    $doc = new DOMDocument();
    $doc->loadHTML($content, );
    $imgs = $doc->getElementsByTagName('img');
    for($i = $imgs->length; --$i >= 0;){
        $node = $imgs->item($i);
        if (strpos($node->getAttribute('src'), $featured_image) !== false) {
            $node->parentNode->removeChild($node);
        }
    }
    return $doc->savehtml();
});
```