oauth2: drop pre-1.4 workaround

Change-Id: Icac33569b4937602b0aac46ec36cc85b5aa53877
Reviewed-on: https://go-review.googlesource.com/6071
Reviewed-by: Andrew Gerrand <adg@golang.org>

example_test.go

@@ -7,15 +7,10 @@ package oauth2_test
 import (
 	"fmt"
 	"log"
-	"testing"
 
 	"golang.org/x/oauth2"
 )
 
-// TODO(jbd): Remove after Go 1.4.
-// Related to https://codereview.appspot.com/107320046
-func TestA(t *testing.T) {}
-
 func ExampleConfig() {
 	conf := &oauth2.Config{
 		ClientID:     "YOUR_CLIENT_ID",