Fix order by on is_primary.

Fix order by on is_primary.

As pointed out in https://lab.civicrm.org/dev/mail/issues/26 the order by is not the
correct format for order_by and has no effect. I tested to make sure it was not
some magic.

I opted for (implict) ASC as the order by for non sms is ASC and further down
processing seems to overwrite each row as it happens so primary later
would overwrite earlier