Use table/index_close() more consistently

Use table/index_close() more consistently

All the code paths updated here have been using relation_close() to
close a relation that has already been opened with table_open() or
index_open(), where a relkind check is enforced.

table_close() and index_open() do the same thing as relation_close(), so
there was no harm, but being inconsistent could lead to issues if the
internals of these close() functions begin to introduce some logic
specific to each relkind in the future.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/aUKamYGiDKO6byp5@ip-10-97-1-34.eu-west-3.compute.internal