pgsql: Remove obsolete SAMESIGN macro

Remove obsolete SAMESIGN macro

The SAMESIGN macro was historically used as a helper for manual
integer overflow checks.  However, since commit 4d6ad3125 introduced
overflow-aware integer operations, this manual sign-checking logic is
no longer necessary.

The macro remains defined in brin_minmax_multi.c and timestamp.c, but
is not used in either file.  This patch removes these definitions to
clean things up.

Author: Richard Guo <guofenglinux@gmail.com>
Discussion: https://postgr.es/m/CAMbWs4-NL3J3hQ3LzrwV-YUkQC18P+jM7ZiegQyAHzgdZev2qg@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/ce1c17a3163fa5adaa7c6af90bb1b0164cc7a28f

Modified Files
--------------
src/backend/access/brin/brin_minmax_multi.c | 2 --
src/backend/utils/adt/timestamp.c           | 2 --
2 files changed, 4 deletions(-)