Remove check for accept() argument types

Remove check for accept() argument types

This check was used to accommodate a staggering variety in particular
in the type of the third argument of accept().  This is no longer of
concern on currently supported systems.  We can just use socklen_t in
the code and put in a simple check that substitutes int for socklen_t
if it's missing, to cover the few stragglers.

Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/3538f4c4-1886-64f2-dcff-aaad8267fb82@enterprisedb.com