metabox-bbpress.css?ver=3.5 • Unnecessary CSS Link?

SEO-Plugin: 1.3.4.3
No BBPress installed
Website: hamacama

My 404 Logger (Redirection) shows that people access:
​/wp-content​/plugins​/wordpress-seo​/css​/metabox-bbpress.css?ver=3.5
and this request results in 404.

Thanks for helping

http://wordpress.org/extend/plugins/wordpress-seo/