pgsql: Remove IS_AF_UNIX macro

Remove IS_AF_UNIX macro

The AF_UNIX macro was being used unprotected by HAVE_UNIX_SOCKETS,
apparently since 2008. So the redirection through IS_AF_UNIX() is
apparently no longer necessary. (More generally, all supported
platforms are now HAVE_UNIX_SOCKETS, but even if there were a new
platform in the future, it seems plausible that it would define the
AF_UNIX symbol even without kernel support.) So remove the
IS_AF_UNIX() macro and make the code a bit more consistent.

Discussion: https://www.postgresql.org/message-id/flat/f2d26815-9832-e333-d52d-72fbc0ade896%40enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/797129e5910144a2a937b88e145874a15b83578a

Modified Files
--------------
src/backend/libpq/hba.c | 4 ++--
src/backend/libpq/pqcomm.c | 24 ++++++++++++------------
src/backend/postmaster/postmaster.c | 4 ++--
src/include/common/ip.h | 6 ------
src/interfaces/libpq/fe-connect.c | 14 +++++++-------
5 files changed, 23 insertions(+), 29 deletions(-)