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 a1789986227cd5cc8f0ee48c41fcd96c8140f286..f81a01145790286917e96efa797307e807ffd959 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;
   virtual void OnMessage(const std::string& msg) {}
   virtual void OnSignalingMessage(const std::string& msg) {}