Open Graph: add WP SEO back to the list of conflicting plugins

WP SEO uses `remove_action( 'wp_head', 'jetpack_og_tags' );` to remove JP's OG tags:
https://github.com/Yoast/wordpress-seo/blob/master/frontend/class-opengraph.php#L60

But that won't work. They'll need to use the `jetpack_enable_open_graph` filter instead. I sent them a Pull Request to change this (see Yoast/wordpress-seo#1374).

In the meantime, this commit adds WP SEO back to the list of conflicting plugins until the filter is changed in WP SEO.