Trim ORDER BY/DISTINCT aggregate pathkeys in gather_grouping_paths
Similar to
d8a295389, trim off any PathKeys which are for ORDER BY /
DISTINCT aggregate functions from the PathKey List for the Gather Merge
paths created by gather_grouping_paths(). These additional PathKeys are
not valid to use after grouping has taken place as these PathKeys belong
to columns which are inputs to an aggregate function and, therefore are
unavailable after aggregation.
Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/
cf63174c-8c89-3953-cb49-
48f41f74941a@gmail.com
Backpatch-through: 16, where
1349d2790 was added