Revert "cmd/go/internal/test: wrap os.Stdout always"

This reverts CL 400877.

Reason for revert: broke TestScript/test_output_wait and the
regression test for #18153 on certain builders.

Fixes #52461.

Change-Id: I98627ce5e22088b0784be502c459480c41ba353a
Reviewed-on: https://go-review.googlesource.com/c/go/+/401494
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/cmd/go/internal/test/test.go

@@ -1261,11 +1261,7 @@ func (c *runCache) builderRunTest(b *work.Builder, ctx context.Context, a *work.
 		return nil
 	}
 
-	// The os/exec package treats an *os.File differently to an io.Writer.
+	var stdout io.Writer = os.Stdout
-	// Embed os.Stdout in an io.Writer struct so that we get the same
-	// behavior regardless of whether we wrap it below.
-	// See golang.org/issue/24050
-	var stdout io.Writer = struct{ io.Writer }{os.Stdout}
 	var err error
 	if testJSON {
 		json := test2json.NewConverter(lockedStdout{}, a.Package.ImportPath, test2json.Timestamp)

src/cmd/go/testdata/script/test_output_wait.txt

@@ -1,35 +0,0 @@
-# Wait for test output from sub-processes whether or not the package name is
-# provided on the command-line.
-go test -v
-stdout 'PASS\s+WAIT\s+ok'
-go test -v .
-stdout 'PASS\s+WAIT\s+ok'
-
--- go.mod --
-module x
-
--- x_test.go --
-package x
-
-import (
-	"os"
-	"os/exec"
-	"testing"
-)
-
-func TestMain(m *testing.M) {
-	if os.Getenv("WAIT") == "true" {
-		os.Stdout.Write([]byte("WAIT\n"))
-		return
-	}
-	m.Run()
-}
-
-func TestWait(t *testing.T) {
-	cmd := exec.Command(os.Args[0])
-	cmd.Env = []string{"WAIT=true"}
-	cmd.Stdout = os.Stdout
-	if err := cmd.Start(); err != nil {
-		t.Fatal(err)
-	}
-}