vacuumdb: Fix --missing-stats-only for partitioned indexes.

vacuumdb: Fix --missing-stats-only for partitioned indexes.

The current form of the catalog query picks up partitioned tables
with expression indexes that lack statistics.  However, since such
indexes never have statistics, there's no point in analyzing them.
To fix, adjust the relevant part of the query to skip partitioned
tables with expression indexes.  While at it, remove the nearby
stainherit check; entries for index expressions always have
stainherit = false.

Author: Baji Shaik <baji.pgdev@gmail.com>
Reviewed-by: Corey Huinker <corey.huinker@gmail.com>
Discussion: https://postgr.es/m/CA%2Bfm-RPE1tEc6CUUPDyRbYTz9tF5Kw47nnk-Zq%3DyYvanbsxyCQ%40mail.gmail.com
Backpatch-through: 18