How do I str_replace with template tag?

This function will return the featured image without the class attribute:

function wpse239577_post_thumbnail( $image_size="full" ) {
    $image_id = get_post_thumbnail_id();
    $image = wp_get_attachment_image_src( $image_id, $image_size );
    if ( ! $image ) {
        return false;
    }

    return '<img src="' . esc_url(  $image[0] ) . '" alt="" />';
}

Usage: echo wpse239577_post_thumbnail(); The $size parameter is a WordPress image size and is optional.

Also, the_post_thumbmail() already echos its output so echo is unnecessary. get_the_post_thumbmail() is similar, but it returns the output.