unix: drop fallback to utimes in UtimesNano on Linux

Same as CL 346790 does for package syscall.

The minimum required Linux kernel version for Go 1.18 will be changed to
2.6.32, see golang/go#45964. The current minimum required version is
2.6.23 and utimensat was added in 2.6.22, so the fallback isn't even
necessary for the current minimum supported version. Remove the fallback
to utimes.

For golang/go#45964

Change-Id: Iaed782d182851c9ccff32f831e1704bae52662a6
Reviewed-on: https://go-review.googlesource.com/c/sys/+/346829
Trust: Tobias Klauser <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Matt Layher <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: tklauser

unix/syscall_linux.go

@@ -168,27 +168,7 @@ func Utimes(path string, tv []Timeval) error {
 //sys	utimensat(dirfd int, path string, times *[2]Timespec, flags int) (err error)
 
 func UtimesNano(path string, ts []Timespec) error {
-	if ts == nil {
-		err := utimensat(AT_FDCWD, path, nil, 0)
-		if err != ENOSYS {
-			return err
-		}
-		return utimes(path, nil)
-	}
-	if len(ts) != 2 {
-		return EINVAL
-	}
-	err := utimensat(AT_FDCWD, path, (*[2]Timespec)(unsafe.Pointer(&ts[0])), 0)
-	if err != ENOSYS {
-		return err
-	}
-	// If the utimensat syscall isn't available (utimensat was added to Linux
-	// in 2.6.22, Released, 8 July 2007) then fall back to utimes
-	var tv [2]Timeval
-	for i := 0; i < 2; i++ {
-		tv[i] = NsecToTimeval(TimespecToNsec(ts[i]))
-	}
-	return utimes(path, (*[2]Timeval)(unsafe.Pointer(&tv[0])))
+	return UtimesNanoAt(AT_FDCWD, path, ts, 0)
 }
 
 func UtimesNanoAt(dirfd int, path string, ts []Timespec, flags int) error {