Remove superfluous MkdirAll from MakeTempDirOrDie

After the call to ioutil.TempDir, the directory has already been
created, and MkdirAll therefore can't do anything.  The mode argument
in particular is misleading.

test/utils/tmpdir.go

@@ -18,7 +18,6 @@ package utils
 
 import (
 	"io/ioutil"
-	"os"
 
 	"github.com/golang/glog"
 )
@@ -31,8 +30,5 @@ func MakeTempDirOrDie(prefix string, baseDir string) string {
 	if err != nil {
 		glog.Fatalf("Can't make a temp rootdir: %v", err)
 	}
-	if err = os.MkdirAll(tempDir, 0750); err != nil {
-		glog.Fatalf("Can't mkdir(%q): %v", tempDir, err)
-	}
 	return tempDir
 }