Commit fe27009c tried to make parallel.c's Windows implementation of
piperead() translate Windows socket errors to Unix, but that didn't
actually work because TranslateSocketError() is backend-internal code
(and not even public there).  But on closer inspection, the sole
caller of this function doesn't actually care whether the result is
zero or negative, much less inspect the errno.  So the whole exercise
is totally useless, and has been since this code was introduced.
Rip it out and just call recv() directly.

Per buildfarm.

Discussion: https://postgr.es/m/2621622.1602184554@sss.pgh.pa.us