chore(pubsub): fix small lingering TODO comments (#4004)

* fix(pubsub): fix failing message storage policy tests

* chore(pubsub): fix small lingering TODO comments

* revert to strings.Replace

pubsub/integration_test.go

@@ -1603,10 +1603,7 @@ func TestIntegration_BadEndpoint(t *testing.T) {
 func TestIntegration_Filter_CreateSubscription(t *testing.T) {
 	t.Parallel()
 	ctx := context.Background()
-	// TODO(hongalex): Remove this once filtering is GA.
-	// https://github.com/googleapis/google-cloud-go/issues/2390
-	opts := withGRPCHeadersAssertion(t, option.WithEndpoint("staging-pubsub.sandbox.googleapis.com:443"))
-	client := integrationTestClient(ctx, t, opts...)
+	client := integrationTestClient(ctx, t)
 	defer client.Close()
 	topic, err := client.CreateTopic(ctx, topicIDs.New())
 	if err != nil {