pgsql: Remove dead code for temporary relations in partition planning

Remove dead code for temporary relations in partition planning

Since recent commit 1c7c317c, temporary relations cannot be mixed with
permanent relations within the same partition tree, and the same counts
for temporary relations created by other sessions, which the planner
simply discarded. Instead be paranoid and issue an error, as those
should be blocked at definition time, at least for now.

At the same time, a test case is added to stress what has been moved
when expand_partitioned_rtentry gets called recursively but bumps on a
partitioned relation with no partitions which should be handled the same
way as the non-inheritance case. This code may be reworked in a close
future, and covering this code path will limit surprises.

Reported-by: David Rowley
Author: David Rowley
Reviewed-by: Amit Langote, Robert Haas, Michael Paquier
Discussion: https://postgr.es/m/CAKJS1f_HyV1txn_4XSdH5EOhBMYaCwsXyAj6bHXk9gOu4JKsbw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fc057b2b8fc3c3556d9f8cc0195c622aaad92c9e

Modified Files
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src/backend/optimizer/prep/prepunion.c | 33 ++++++++++++++++-----------------
src/test/regress/expected/select.out | 13 +++++++++++++
src/test/regress/sql/select.sql | 8 ++++++++
3 files changed, 37 insertions(+), 17 deletions(-)