wp_title() function in <title> tag

Question

I have used the following code in functions.php to retrieve the title of my WordPress Theme which is being got ready for Themeforest release.

add_theme_support( 'title-tag' );

And then I have used the code below (functions.php) as a backwards compatibility for older versions:

 if ( ! function_exists( '_wp_render_title_tag' ) ) {
        function theme_slug_render_title() {
    ?>
    <title><?php wp_title( '|', true, 'right' ); ?></title>
    <?php
        }
        add_action( 'wp_head', 'theme_slug_render_title' );
    }

Well, everything is OK for Theme Check Plugin as the plugin doesn’t indicate any warnings, requirements, recommendations, info etc.

But the themecheck.org which is an online service for theme check indicates a CRITICAL ALERT like this:

Title : Title The tags can only contain a call to wp_title(). Use the wp_title filter to modify the output.

I have figured it out that the second code snippet causes this ALERT. If I remove this code, then it is OK for themecheck.org.

As far as I know that wp_title() is a required function in Themeforest WordPress Theme.

And now, I would like to know

1. What if I use the two codes simultaneously? Is there any chance to get rejection (hard/soft) in Themeforest?
2. What if I remove the backwards compatibility code, the second code snippet?

Thanks a lot for reading. 