Delete MediaTransport method SetNetworkChangeCallback

Followup to https://webrtc-review.googlesource.com/c/src/+/121460.

Bug: webrtc:9719
Change-Id: I6261c450379de22d916f4048fec89e5e67e300f8
Reviewed-on: https://webrtc-review.googlesource.com/c/121651
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Peter Slatala <psla@webrtc.org>
Commit-Queue: Peter Slatala <psla@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26576}
diff --git a/api/DEPS b/api/DEPS
index 9bb179a..96fd36b 100644
--- a/api/DEPS
+++ b/api/DEPS
@@ -111,7 +111,6 @@
   "media_transport_interface\.h": [
     "+rtc_base/copy_on_write_buffer.h",  # As used by datachannelinterface.h
     "+rtc_base/network_route.h",
-    "+rtc_base/deprecation.h",
   ],
 
   "peer_connection_factory_proxy\.h": [
diff --git a/api/media_transport_interface.cc b/api/media_transport_interface.cc
index a02356e..571e82b 100644
--- a/api/media_transport_interface.cc
+++ b/api/media_transport_interface.cc
@@ -154,9 +154,6 @@
   return absl::nullopt;
 }
 
-void MediaTransportInterface::SetNetworkChangeCallback(
-    MediaTransportNetworkChangeCallback* callback) {}
-
 void MediaTransportInterface::AddNetworkChangeCallback(
     MediaTransportNetworkChangeCallback* callback) {}
 
diff --git a/api/media_transport_interface.h b/api/media_transport_interface.h
index cc97b35..1266000 100644
--- a/api/media_transport_interface.h
+++ b/api/media_transport_interface.h
@@ -29,7 +29,6 @@
 #include "api/units/data_rate.h"
 #include "api/video/encoded_image.h"
 #include "rtc_base/copy_on_write_buffer.h"
-#include "rtc_base/deprecation.h"
 #include "rtc_base/network_route.h"
 
 namespace rtc {
@@ -429,16 +428,10 @@
   // might not be a very accurate number.
   virtual size_t GetAudioPacketOverhead() const;
 
-  // Sets an observer for network change events. If the network route is already
-  // established when the callback is set, |callback| will be called immediately
-  // with the current network route.
-  // Before media transport is destroyed, the callback must be unregistered by
-  // setting it to nullptr.
-  // TODO(nisse): The SetNetworkChangeCallback is being replaced with Add/Remove
-  // methods, because both video channel and voice channel need to register.
-  RTC_DEPRECATED
-  virtual void SetNetworkChangeCallback(
-      MediaTransportNetworkChangeCallback* callback);
+  // Registers an observer for network change events. If the network route is
+  // already established when the callback is added, |callback| will be called
+  // immediately with the current network route. Before media transport is
+  // destroyed, the callback must be removed.
   virtual void AddNetworkChangeCallback(
       MediaTransportNetworkChangeCallback* callback);
   virtual void RemoveNetworkChangeCallback(