MySQL optimiser seems to prefer a full table scan of `post-user`
table in the count query mentioned in issue #14763. When the origin
and deleted columns are added to the index, the IN-query part of
the query can be done with index-only scan, which is much faster.
Adding the columns in the order
uri-id, origin, deleted
allows some other queries to also use it when checking
for uri-id and origin.
Fixes#14763
