remove Config.MaxRetryTokenAge, set it to the handshake timeout (#4064)

There is no good reason to manually set the validity period for Retry
tokens. Retry tokens are only valid on a single connection during the
handshake, so it makes sense to limit their validity to the configured
handshake timeout.

config_test.go

@@ -80,8 +80,6 @@ var _ = Describe("Config", func() {
 				f.Set(reflect.ValueOf(time.Hour))
 			case "MaxTokenAge":
 				f.Set(reflect.ValueOf(2 * time.Hour))
-			case "MaxRetryTokenAge":
-				f.Set(reflect.ValueOf(2 * time.Minute))
 			case "TokenStore":
 				f.Set(reflect.ValueOf(NewLRUTokenStore(2, 3)))
 			case "InitialStreamReceiveWindow":