Remove addresses sitemap from sitemap index

As sitemaps indices are not allowed to have other sitemap indices, we need to adapt our sitemap service to reflect that. See https://productforums.google.com/forum/#!topic/webmasters/6UyJ3pfRXZk and the related PR @ https://github.com/geoadmin/mf-geoadmin3/pull/1566
minor I would use `in_index` instead, we already have `multi_part`...
FYI:
I usually use camel case for input parameters, but it is not clearly defined.