Remove use of deprecated net.Error.Temporary (#1589)

net.Error.Temporary has been deprecated since Go 1.18. There
has been some discussion around what to use in server accept loops
instead [1], but the suggestion seems to be that it may be a mistake
to have any sort of retries in place [2].

This PR removes it, which may expose some users to errors that were
previously swallowed and retried, but at the expense of leaking file
descriptors and the like.

1: https://groups.google.com/g/golang-nuts/c/-JcZzOkyqYI/m/xwaZzjCgAwAJ?pli=1
2: https://groups.google.com/g/golang-nuts/c/-JcZzOkyqYI/m/vNNiVn_LAwAJ

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

server.go

@@ -476,9 +476,6 @@ func (srv *Server) serveTCP(l net.Listener) error {
 			if !srv.isStarted() {
 				return nil
 			}
-			if neterr, ok := err.(net.Error); ok && neterr.Temporary() {
-				continue
-			}
 			return err
 		}
 		srv.lock.Lock()
@@ -535,9 +532,6 @@ func (srv *Server) serveUDP(l net.PacketConn) error {
 			if !srv.isStarted() {
 				return nil
 			}
-			if netErr, ok := err.(net.Error); ok && netErr.Temporary() {
-				continue
-			}
 			return err
 		}
 		if len(m) < headerSize {