unix: rm unused zos test helper functions

These functions are not used anywhere in zos tests.

Checked with:

	git grep -wE 'mktmpfifo|touch|chtmpdir' \
		$(git grep -lw zos | grep _test.go; ls *_zos_test.go)

Change-Id: Ie8b25640578e1c607dd4e4f0fe4e7869f8e3f5d3
Reviewed-on: https://go-review.googlesource.com/c/sys/+/526296
Reviewed-by: Tobias Klauser <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dustin Ward <[email protected]>

Author: kolyshkin

unix/syscall_zos_test.go

@@ -553,59 +553,6 @@ func TestMkdev(t *testing.T) {
 	}
 }
 
-// mktmpfifo creates a temporary FIFO and provides a cleanup function.
-func mktmpfifo(t *testing.T) (*os.File, func()) {
-	err := unix.Mkfifo("fifo", 0666)
-	if err != nil {
-		t.Fatalf("mktmpfifo: failed to create FIFO: %v", err)
-	}
-
-	f, err := os.OpenFile("fifo", os.O_RDWR, 0666)
-	if err != nil {
-		os.Remove("fifo")
-		t.Fatalf("mktmpfifo: failed to open FIFO: %v", err)
-	}
-
-	return f, func() {
-		f.Close()
-		os.Remove("fifo")
-	}
-}
-
-// utilities taken from os/os_test.go
-
-func touch(t *testing.T, name string) {
-	f, err := os.Create(name)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if err := f.Close(); err != nil {
-		t.Fatal(err)
-	}
-}
-
-// chtmpdir changes the working directory to a new temporary directory and
-// provides a cleanup function. Used when PWD is read-only.
-func chtmpdir(t *testing.T) func() {
-	oldwd, err := os.Getwd()
-	if err != nil {
-		t.Fatalf("chtmpdir: %v", err)
-	}
-	d, err := ioutil.TempDir("", "test")
-	if err != nil {
-		t.Fatalf("chtmpdir: %v", err)
-	}
-	if err := os.Chdir(d); err != nil {
-		t.Fatalf("chtmpdir: %v", err)
-	}
-	return func() {
-		if err := os.Chdir(oldwd); err != nil {
-			t.Fatalf("chtmpdir: %v", err)
-		}
-		os.RemoveAll(d)
-	}
-}
-
 func TestMountUnmount(t *testing.T) {
 	// use an available fs
 	var buffer struct {