The es_es lang pack (containing 55 changes from es) was previously removed from the downloads page in December 2006 following a discussion https://moodle.org/mod/forum/discuss.php?d=58860 and a vote. Thus, it is not listed in http://download.moodle.org/langpack/1.6/.
It then somehow reappeared, perhaps during the change from CVS to AMOS and is listed as an available language pack for all 2.x versions. There is no es_es maintainer in AMOS i.e. the lang pack remains unchanged from 2006. Thus it seems sensible to remove it once again from the downloads page and also to remove it from AMOS.