Delete deprecated PeerConnection methods, and corresponding using declarations.

webrtc/pc/peerconnectionfactory_unittest.cc

Index: webrtc/pc/peerconnectionfactory_unittest.cc
diff --git a/webrtc/pc/peerconnectionfactory_unittest.cc b/webrtc/pc/peerconnectionfactory_unittest.cc
index 9a6e54310580037e3f911b85e3fb44168455b811..10aacc0194e463139987cfb76b977b70e8a21e3c 100644
--- a/webrtc/pc/peerconnectionfactory_unittest.cc
+++ b/webrtc/pc/peerconnectionfactory_unittest.cc
@@ -63,13 +63,6 @@ static const char kTurnIceServerWithIPv6Address[] =
 
 class NullPeerConnectionObserver : public PeerConnectionObserver {
  public:
-  // We need these using declarations because there are two versions of each of
-  // the below methods and we only override one of them.
-  // TODO(deadbeef): Remove once there's only one version of the methods.
-  using PeerConnectionObserver::OnAddStream;
-  using PeerConnectionObserver::OnRemoveStream;
-  using PeerConnectionObserver::OnDataChannel;
-
   virtual ~NullPeerConnectionObserver() = default;
   void OnSignalingChange(
       PeerConnectionInterface::SignalingState new_state) override {}