pgsql: Remove configure probe for netinet/tcp.h.

Remove configure probe for netinet/tcp.h.

<netinet/tcp.h> is in SUSv3 and all targeted Unix systems have it.
For Windows, we can provide a stub include file, to avoid some #ifdef
noise.

Discussion: https://postgr.es/m/CA+hUKGKErNfhmvb_H0UprEmp4LPzGN06yR2_0tYikjzB-2ECMw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2492fe49dcb534844d9eece97504b4caca1d81ae

Modified Files
--------------
configure                                | 2 +-
configure.ac                             | 1 -
src/backend/libpq/be-secure-openssl.c    | 2 --
src/backend/libpq/be-secure.c            | 2 --
src/backend/libpq/ifaddr.c               | 2 --
src/backend/libpq/pqcomm.c               | 2 --
src/common/ip.c                          | 2 --
src/include/libpq/libpq-be.h             | 2 --
src/include/pg_config.h.in               | 3 ---
src/include/port/win32/netinet/tcp.h     | 7 +++++++
src/interfaces/libpq/fe-connect.c        | 2 --
src/interfaces/libpq/fe-protocol3.c      | 2 --
src/interfaces/libpq/fe-secure-openssl.c | 2 --
src/interfaces/libpq/fe-secure.c         | 2 --
src/tools/msvc/Solution.pm               | 1 -
15 files changed, 8 insertions(+), 26 deletions(-)