FB Events: use event URL where possible

add_filter( 'tribe_get_event_website_url', 'event_website_use_fb_event_url', 10, 2 );

function event_website_use_fb_event_url( $url, $id ) {
    $fb_id = get_post_meta( $id, '_FacebookID', true );
    if ( empty( $fb_id ) ) return $url;
    return esc_url( 'http://facebook.com/events/' . $fb_id );
}