Fix vet

Author: arjan-bal

experimental/credentials/credentials_test.go

@@ -41,13 +41,6 @@ func Test(t *testing.T) {
 	grpctest.RunSubTests(t, s{})
 }
 
-// A struct that implements AuthInfo interface but does not implement GetCommonAuthInfo() method.
-type testAuthInfoNoGetCommonAuthInfoMethod struct{}
-
-func (ta testAuthInfoNoGetCommonAuthInfoMethod) AuthType() string {
-	return "testAuthInfoNoGetCommonAuthInfoMethod"
-}
-
 // A struct that implements AuthInfo interface and implements CommonAuthInfo() method.
 type testAuthInfo struct {
 	credentials.CommonAuthInfo