pgsql: Fix outdated references to guc.c

Fix outdated references to guc.c

Commit 0a20ff54f split out the GUC variables from guc.c into a new file
guc_tables.c. This updates comments referencing guc.c regarding variables
which are now in guc_tables.c.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/6B50C70C-8C1F-4F9A-A7C0-EEAFCC032406@yesql.se

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7ab1bc2939f32aa995bdb81eaac3bb28f908e980

Modified Files
--------------
src/backend/commands/variable.c               | 2 +-
src/backend/libpq/be-secure-openssl.c         | 3 ++-
src/backend/storage/lmgr/predicate.c          | 6 +++---
src/bin/pg_dump/dumputils.c                   | 2 +-
src/include/miscadmin.h                       | 2 +-
src/test/modules/test_misc/t/003_check_guc.pl | 8 ++++----
src/timezone/pgtz.c                           | 2 +-
7 files changed, 13 insertions(+), 12 deletions(-)