Cleanup more code related to ws2_32.dll loading in src/port/getaddrinfo.c

Cleanup more code related to ws2_32.dll loading in src/port/getaddrinfo.c

e2e0219 has removed a code path for Windows 2000 that attempts to load
wship6.dll as fallback if ws2_32.dll is found but not getaddrinfo(),
leaving behind a dangling pointer as the library is freed.  However,
there is no point in this check as ws2_32.dll exists since Windows XP,
so just remove the duplicated check.

Reported-by: Tom Lane
Discussion: https://postgr.es/m/9781.1582146114@sss.pgh.pa.us