pgsql: Remove unused global variables

Remove unused global variables

The new clang 23 has a new warning about set-but-unused
static (internal-linkage) global variables: -Wunused-but-set-global,
which is activated in PostgreSQL builds via -Wall. This triggers a
few warnings in PostgreSQL code. This commit removes several such
variables that were either never used or whose last use was removed
some time ago.

Reviewed-by: Andreas Karlsson <andreas(at)proxel(dot)se>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://www.postgresql.org/message-id/flat/eb013f9d-2247-444e-8815-9d17b4ce78e7%40eisentraut.org

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e8601cb3d48de06e642683e91ef21f528e2ab462

Modified Files
--------------
src/backend/access/transam/xlog.c | 10 ----------
src/backend/postmaster/postmaster.c | 3 ---
src/bin/pg_dump/pg_dump_sort.c | 2 --
src/test/modules/test_resowner/test_resowner_many.c | 6 +-----
4 files changed, 1 insertion(+), 20 deletions(-)