all: call flag.Parse from TestMain only if used

These don't use any flags in TestMain itself, so the call is redundant
as M.Run will do it.

Change-Id: I00f2ac7f846dc2c3ad3535eb8177616b2d900149
Reviewed-on: https://go-review.googlesource.com/33275
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/go_test.go

@@ -6,7 +6,6 @@ package main_test
 
 import (
 	"bytes"
-	"flag"
 	"fmt"
 	"go/build"
 	"go/format"
@@ -67,8 +66,6 @@ func init() {
 // The TestMain function creates a go command for testing purposes and
 // deletes it after the tests have been run.
 func TestMain(m *testing.M) {
-	flag.Parse()
-
 	if canRun {
 		args := []string{"build", "-tags", "testgo", "-o", "testgo" + exeSuffix}
 		if race.Enabled {

src/cmd/objdump/objdump_test.go

@@ -21,7 +21,6 @@ import (
 var tmp, exe string // populated by buildObjdump
 
 func TestMain(m *testing.M) {
-	flag.Parse()
 	if !testenv.HasGoBuild() {
 		return
 	}

src/cmd/vet/vet_test.go

@@ -6,7 +6,6 @@ package main_test
 
 import (
 	"bytes"
-	"flag"
 	"fmt"
 	"internal/testenv"
 	"os"
@@ -24,7 +23,6 @@ const (
 
 // We implement TestMain so remove the test binary when all is done.
 func TestMain(m *testing.M) {
-	flag.Parse()
 	result := m.Run()
 	os.Remove(binary)
 	os.Exit(result)