Throw a more on-point error for publications depending on columns.

Throw a more on-point error for publications depending on columns.

Same as 42b041243, except that the trouble case is a publication
WHERE clause that depends on a column.

Again reported by Alexander Lakhin.  Back-patch to v15 where
we added publication WHERE clauses.

Discussion: https://postgr.es/m/548a47bc-87ae-b3df-c6a2-60b9966f808b@gmail.com