Featured Content: Remove default value.
This should not cause any headaches with existing installs, since it never worked outside of Twenty Fourteen.
props @obenland
Likes: Avoid a PHP Notice when $_POST['post_type'] is not set in the meta_box_save function.
props @jblz
Jetpack Likes: Make sure save like meta box options for attachments too, and switch to using a list of public post types vs. just post|page so that it's forward compatible should we add other post types to wpcom in the future.
Props @dllh