Fix issue with deprecated CongestionController interface not working.

webrtc/modules/congestion_controller/include/congestion_controller.h

Index: webrtc/modules/congestion_controller/include/congestion_controller.h
diff --git a/webrtc/modules/congestion_controller/include/congestion_controller.h b/webrtc/modules/congestion_controller/include/congestion_controller.h
index f2bec76f2523c175b90577f24c72f3a1c56040c2..1f070359aa88e937cc39a2933a5eb94483a6d207 100644
--- a/webrtc/modules/congestion_controller/include/congestion_controller.h
+++ b/webrtc/modules/congestion_controller/include/congestion_controller.h
@@ -47,17 +47,10 @@ class CongestionController : public CallStatsObserver, public Module {
   // packet headers and is measured in bits per second.
   class Observer {
    public:
-    // This is to be deprecated. Please use the one below instead.
-    RTC_DEPRECATED virtual void OnNetworkChanged(uint32_t bitrate_bps,
-                                                 uint8_t fraction_loss,
-                                                 int64_t rtt_ms) {}
-
-    // TODO(minyue): make this method pure virtual when all uses of the old API
-    // have been updated.
     virtual void OnNetworkChanged(uint32_t bitrate_bps,
                                   uint8_t fraction_loss,  // 0 - 255.
                                   int64_t rtt_ms,
-                                  int64_t probing_interval_ms) {}
+                                  int64_t probing_interval_ms) = 0;
 
    protected:
     virtual ~Observer() {}