BasicAsyncResolverFactoryTest: fix leak.

This change removes a memory leak from a faulty test.
It's unknown why this leak doesn't trigger the leak
checker, see the referred bug for further info.

Bug: webrtc:11605
Change-Id: I05979a696352ed2bc90cd029e462788c0912e02d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/175919
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31348}

p2p/base/basic_async_resolver_factory_unittest.cc

@@ -30,6 +30,7 @@ class BasicAsyncResolverFactoryTest : public ::testing::Test,
     rtc::SocketAddress address("", 0);
     resolver->Start(address);
     ASSERT_TRUE_WAIT(address_resolved_, 10000 /*ms*/);
+    resolver->Destroy(false);
   }
 
   void SetAddressResolved(rtc::AsyncResolverInterface* resolver) {