folly/experimental/test/FutureDAGTest.cpp: fix ASAN-detected heap use-after-free

Summary: Building/testing with ASAN would elicit a heap use-after-free.

Differential Revision: D3639117

fbshipit-source-id: 30b5fa7d3fe1d804c4fba5bada8197a3a05a8333

folly/experimental/test/FutureDAGTest.cpp

@@ -123,6 +123,7 @@ TEST_F(FutureDAGTest, RemoveNodeComplex) {
   dependency(h2, h1);
   remove(h1);
   remove(h2);
+  remove(h3);
   ASSERT_NO_THROW(dag->go().get());
   checkOrder();
 }