pkg/testutil: drop go1.4 goroutine leak exception

pkg/testutil/leak.go

@@ -74,12 +74,7 @@ func AfterTest(t *testing.T) {
 		"timeoutHandler":                               "a TimeoutHandler",
 		"net.(*netFD).connect(":                        "a timing out dial",
 		").noteClientGone(":                            "a closenotifier sender",
-	}
-
-	// readLoop was buggy before go1.5:
-	// https://github.com/golang/go/issues/10457
-	if getAtLeastGo15() {
-		badSubstring[").readLoop("] = "a Transport"
+		").readLoop(":                                  "a Transport",
 	}
 
 	var stacks string
@@ -126,11 +121,3 @@ func interestingGoroutines() (gs []string) {
 	sort.Strings(gs)
 	return
 }
-
-// getAtLeastGo15 returns true if the runtime has go1.5+.
-func getAtLeastGo15() bool {
-	var major, minor int
-	var discard string
-	i, err := fmt.Sscanf(runtime.Version(), "go%d.%d%s", &major, &minor, &discard)
-	return (err == nil && i == 3 && (major > 1 || major == 1 && minor >= 5))
-}