net: mark TestDialerDualStack as flaky

It was already marked flaky for everything but the dashboard.
Remove that restriction. It's just flaky overall.

It's doing more harm than good.

Updates #13324

Change-Id: I36feff32a1b8681e77700f74b9c70cb4073268eb
Reviewed-on: https://go-review.googlesource.com/38459
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/net/dial_test.go

@@ -715,11 +715,8 @@ func TestDialerLocalAddr(t *testing.T) {
 }
 
 func TestDialerDualStack(t *testing.T) {
-	// This test is known to be flaky. Don't frighten regular
-	// users about it; only fail on the build dashboard.
-	if testenv.Builder() == "" {
-		testenv.SkipFlaky(t, 13324)
-	}
+	testenv.SkipFlaky(t, 13324)
+
 	if !supportsIPv4 || !supportsIPv6 {
 		t.Skip("both IPv4 and IPv6 are required")
 	}