Doc: Abstract AF_UNIX sockets don't work on Windows.

Doc: Abstract AF_UNIX sockets don't work on Windows.

An early release of AF_UNIX in Windows apparently supported Linux-style
"abstract" Unix sockets, but they do not seem to work in current Windows
versions and there is no mention of any of this in the Winsock
documentation.  Remove the mention of Windows from the documentation.

Back-patch to 14, where commit c9f0624b landed.

Discussion: https://postgr.es/m/CA%2BhUKGKrYbSZhrk4NGfoQGT_3LQS5pC5KNE1g0tvE_pPBZ7uew%40mail.gmail.com