pgsql: Cosmetic improvements in setup of planner's per-RTE arrays.

Cosmetic improvements in setup of planner's per-RTE arrays.

Merge setup_append_rel_array into setup_simple_rel_arrays.  There's no
particularly good reason to keep them separate, and it's inconsistent
with the lack of separation in expand_planner_arrays.  The only apparent
benefit was that the fast path for trivial queries in query_planner()
doesn't need to set up the append_rel_array; but all we're saving there
is an if-test and NULL assignment, which surely ought to be negligible.

Also improve some obsolete comments.

Discussion: https://postgr.es/m/17220.1565301350@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1661a4050593a472c369a6660ffec05b6b837c57

Modified Files
--------------
src/backend/optimizer/plan/planmain.c  | 10 +------
src/backend/optimizer/prep/prepunion.c |  8 +----
src/backend/optimizer/util/relnode.c   | 53 ++++++++++++++++++----------------
src/include/nodes/pathnodes.h          |  9 +++---
src/include/optimizer/pathnode.h       |  1 -
5 files changed, 34 insertions(+), 47 deletions(-)