<?php
/*
 * Plugin Name: Jetpack Dont Sync Sitemaps
 * Plugin URI: http://jetpack.com/
 * Description: Don't sync sitemap data
 * Author: Dan Walmsley
 * Version: 0.1
 * License: GPL2+
 * Text Domain: jetpack-dont-sync-sitemaps
 * Domain Path: /languages/
 */
function jetpack_dont_sync_sitemaps( $list ) {
    $sitemap_post_types = array(
        'jp_sitemap_master',
        'jp_sitemap',
        'jp_sitemap_index',
        'jp_img_sitemap',
        'jp_img_sitemap_index',
        'jp_vid_sitemap',
        'jp_vid_sitemap_index',
    );

    $list = (array) $list;
    foreach ( $sitemap_post_types as $post_type ) {
        $list[] = $post_type;
    }
    return $list;
}

add_filter( 'option_jetpack_sync_settings_post_types_blacklist', 'jetpack_dont_sync_sitemaps' );