The new catalog reused a column prefix "sta" from pg_statistic, but this
is undesirable, so change the catalog to use prefix "stx" instead.
Also, rename the column that lists enabled statistic kinds as "stxkind"
rather than "enabled".

Discussion: https://postgr.es/m/CAKJS1f_2t5jhSN7huYRFH3w3rrHfG2QU7hiUHsu-Vdjd1rYT3w@mail.gmail.com