ditch RunWithTimeout test helper

It breaks stack traces on failure.

We can just rely on running `go test -timeout ...` instead, which we
already do in tools/test.

testing/util.go

@@ -6,7 +6,6 @@ import (
 	"reflect"
 	"runtime"
 	"testing"
-	"time"
 
 	"github.com/stretchr/testify/require"
 )
@@ -36,22 +35,6 @@ func stackTrace(all bool) string {
 	return string(buf[:stacklen])
 }
 
-// Borrowed from net/http tests:
-// goTimeout runs f, failing t if f takes more than d to complete.
-func RunWithTimeout(t *testing.T, d time.Duration, f func()) {
-	ch := make(chan bool, 2)
-	timer := time.AfterFunc(d, func() {
-		t.Errorf("Timeout expired after %v: stacks:\n%s", d, stackTrace(true))
-		ch <- true
-	})
-	defer timer.Stop()
-	go func() {
-		defer func() { ch <- true }()
-		f()
-	}()
-	<-ch
-}
-
 // TrimTestArgs finds the first -- in os.Args and trim all args before that
 func TrimTestArgs() {
 	i, l := 0, len(os.Args)