Fix inconsistencies for queries on pg_class in type_sanity.sql

Fix inconsistencies for queries on pg_class in type_sanity.sql

Three queries did not consider partitioned indexes and tables, and
surrounding comments have not been updated in a while.

Like 4b9fbd6be442, this is only cosmetic currently as no such relkinds
exist at this stage of the regression tests, but running these queries
on existing clusters could lead to incorrect results.

Author: Jian He, Michael Paquier
Discussion: https://postgr.es/m/CACJufxGsB1ciahkNDccyxhw-Pfp_-_y+Wx+1BOdRyVVxKojAbg@mail.gmail.com