pgsql: More -Wshadow=compatible-local warning fixes

More -Wshadow=compatible-local warning fixes

In a similar effort to f01592f91, here we're targetting fixing the
warnings where we've deemed the shadowing variable to serve a close enough
purpose to the shadowed variable just to reuse the shadowed version and
not declare the shadowing variable at all.

By my count, this takes the warning count from 106 down to 71.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20220825020839.GT2342@telsasoft.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/3e0fff2e6888e39b0ad5cdfdb78bc1c2bb2b22c9

Modified Files
--------------
src/backend/access/hash/hash_xlog.c       |  1 -
src/backend/access/transam/multixact.c    |  1 -
src/backend/access/transam/xlog.c         |  4 +---
src/backend/commands/functioncmds.c       |  3 ---
src/backend/commands/tablecmds.c          |  1 -
src/backend/commands/vacuum.c             |  2 --
src/backend/executor/execPartition.c      |  1 -
src/backend/executor/nodeWindowAgg.c      |  3 ++-
src/backend/lib/integerset.c              |  2 --
src/backend/libpq/auth.c                  |  2 --
src/backend/optimizer/path/indxpath.c     |  3 +--
src/backend/optimizer/plan/planner.c      | 11 +++--------
src/backend/optimizer/plan/subselect.c    | 10 ----------
src/backend/optimizer/prep/prepunion.c    |  1 -
src/backend/postmaster/autovacuum.c       |  2 +-
src/backend/rewrite/rowsecurity.c         |  1 -
src/backend/statistics/dependencies.c     |  1 -
src/backend/utils/adt/rangetypes_spgist.c |  2 --
src/backend/utils/adt/ruleutils.c         |  3 ---
src/bin/pgbench/pgbench.c                 |  5 -----
20 files changed, 8 insertions(+), 51 deletions(-)