Revert "unix: add Pipe2 on netbsd"

This reverts CL 283593.

Reason for revert: breaks DragonflyBSD builders and was submitted during code freeze.

Change-Id: I784f58ae56f7259d5176921d7a61070e0ac7cb52
Reviewed-on: https://go-review.googlesource.com/c/sys/+/283597
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

unix/pipe2_test.go

@@ -1,55 +0,0 @@
-// Copyright 2021 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build dragonfly freebsd linux netbsd openbsd solaris
-
-package unix_test
-
-import (
-	"testing"
-
-	"golang.org/x/sys/unix"
-)
-
-func TestPipe2(t *testing.T) {
-	const s = "hello"
-	var pipes [2]int
-	err := unix.Pipe2(pipes[:], 0)
-	if err != nil {
-		t.Fatalf("pipe2: %v", err)
-	}
-	r := pipes[0]
-	w := pipes[1]
-	go func() {
-		n, err := unix.Write(w, []byte(s))
-		if err != nil {
-			t.Errorf("bad write: %v", err)
-			return
-		}
-		if n != len(s) {
-			t.Errorf("bad write count: %d", n)
-			return
-		}
-		err = unix.Close(w)
-		if err != nil {
-			t.Errorf("bad close: %v", err)
-			return
-		}
-	}()
-	var buf [10 + len(s)]byte
-	n, err := unix.Read(r, buf[:])
-	if err != nil {
-		t.Fatalf("bad read: %v", err)
-	}
-	if n != len(s) {
-		t.Fatalf("bad read count: %d", n)
-	}
-	if string(buf[:n]) != s {
-		t.Fatalf("bad contents: %s", string(buf[:n]))
-	}
-	err = unix.Close(r)
-	if err != nil {
-		t.Fatalf("bad close: %v", err)
-	}
-}