testutil: remove unused code

It was probably a WIP for something else; it was started in
2016 and not touched since.

testutil/testutil.go

@@ -1,16 +0,0 @@
-package testutil
-
-import "io/ioutil"
-
-// TempName generates a new temporary file name. The caller should
-// remove the temporary file when done.
-func TempName() (string, error) {
-	tmpf, err := ioutil.TempFile("", "transport_cachedkp_")
-	if err != nil {
-		return "", err
-	}
-
-	name := tmpf.Name()
-	tmpf.Close()
-	return name, nil
-}