unix: remove unused stringsFromByteSlice for tests on aix

stringsFromByteSlice is only used in xattr_test.go which isn't enabled
for aix.

Change-Id: I95948cbac285d8efe7f5299de85625cb7541e906
Reviewed-on: https://go-review.googlesource.com/c/sys/+/177839
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>

unix/syscall_aix_test.go

@@ -166,17 +166,3 @@ func TestPselect(t *testing.T) {
 		t.Errorf("Pselect: timeout should have been at least %v, got %v", dur, took)
 	}
 }
-
-// stringsFromByteSlice converts a sequence of attributes to a []string.
-// On Linux, each entry is a NULL-terminated string.
-func stringsFromByteSlice(buf []byte) []string {
-	var result []string
-	off := 0
-	for i, b := range buf {
-		if b == 0 {
-			result = append(result, string(buf[off:i]))
-			off = i + 1
-		}
-	}
-	return result
-}