Update nodeinfo2: Fix the way "active users count" is computed

Previously, only users having MAM messages stored where counted.
Now we count all users who have established a connexion with the server.

nodeinfo2/update_nodeinfo

@@ -45,11 +45,9 @@ per_account_storage_usage() {
 
 user_activity() {
     days_back=${1:-30}
-    sql="select count(distinct username)
-     from archive
-     where peer not like 'irc%'
-     and kind = 'chat'
-     and created_at > current_timestamp - interval '${days_back} days'
+    sql="select count(distinct l.username)
+     from last l
+     where to_timestamp(cast(l.seconds as int)) > current_timestamp - interval '${days_back} days'
      and username not in ('r.giskard', 'lisa.simpson', 'bart.simpson')"
 
     psql -U ejabberd -h localhost ejabberd -c "${sql}" -t | grep -v '^$' | awk '{print $1}'