audio_receive_thread: do not reset onSuccessfulSetup_ while used

Nothing prevents setup() to be used while deleting onSuccessfulSetup_
So checking if (onSuccessfulSetup_) in setup() can cause a crash.
loop_.join() should prevent any call to onSuccessfulSetup_ and
any potential crash

Change-Id: I5fef00edbcc9701a3129a31b247472e62b6453d9

src/media/audio/audio_receive_thread.cpp

@@ -49,7 +49,6 @@ AudioReceiveThread::AudioReceiveThread(const std::string& id,
 
 AudioReceiveThread::~AudioReceiveThread()
 {
-    onSuccessfulSetup_ = nullptr;
     loop_.join();
 }