Change default s.w.org dns-prefetch resource hint value

var_export( $hints );

gave me

array (
  0 => 'https://s.w.org/images/core/emoji/2.4/svg/',
)

so that means the array key is not s.w.org but https://s.w.org/images/core/emoji/2.4/svg/.

Changing the function and using the key of the array with the full url did remove the s.w.org hint while still letting me use resource hints.

function resource_hints( $hints, $relation_type ) {
    if ( 'dns-prefetch' === $relation_type ) {
        // Export the value of the $hints variable
        // to see what is inside of it.
        var_export( $hints );

        // Knowing that the url is not s.w.org but
        // 'https://s.w.org/images/core/emoji/2.4/svg/'
        // I can search for it in the array
        $key = array_search( 'https://s.w.org/images/core/emoji/2.4/svg/', $hints, true );
        if ( false !== $key ) {

                // and here I can unset this key
                unset( $hints[ $key ] );
        }

        // while I can add custom, site specific hints here
        $hints[] = 'http://make.wordpress.org';

    } elseif ( 'prerender' === $relation_type ) {
            $hints[] = 'https://make.wordpress.org/great-again';
    }
    return $hints;
}
add_filter( 'wp_resource_hints', 'resource_hints', 999, 2 );