Delete old "metronome" name, API users should use "decode_metronome".

Now that Chromium has migrated to the new name[1], "decode_metronome",
we can delete the variable with the old name, "metronome".

[1] https://chromium-review.googlesource.com/c/chromium/src/+/5093942

Bug: webrtc:15704
Change-Id: I50fef88a692d83e37af10956b2e12389fa601662
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/330300
Reviewed-by: Markus Handell <handellm@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41331}
diff --git a/api/peer_connection_interface.h b/api/peer_connection_interface.h
index 32aef97..e8dc3dd 100644
--- a/api/peer_connection_interface.h
+++ b/api/peer_connection_interface.h
@@ -1443,10 +1443,6 @@
       transport_controller_send_factory;
   // Metronome used for decoding, must be called on the worker thread.
   std::unique_ptr<Metronome> decode_metronome;
-  // Old name for `decode_metronome`.
-  // TODO(https://crbug.com/webrtc/15704): When callers have migrated to
-  // `decode_metronome`, delete this.
-  std::unique_ptr<Metronome> metronome;
 
   // Media specific dependencies. Unused when `media_factory == nullptr`.
   rtc::scoped_refptr<AudioDeviceModule> adm;
diff --git a/pc/peer_connection_factory.cc b/pc/peer_connection_factory.cc
index 7539282..951da5f 100644
--- a/pc/peer_connection_factory.cc
+++ b/pc/peer_connection_factory.cc
@@ -103,9 +103,7 @@
           (dependencies->transport_controller_send_factory)
               ? std::move(dependencies->transport_controller_send_factory)
               : std::make_unique<RtpTransportControllerSendFactory>()),
-      decode_metronome_(dependencies->decode_metronome
-                            ? std::move(dependencies->decode_metronome)
-                            : std::move(dependencies->metronome)) {}
+      decode_metronome_(std::move(dependencies->decode_metronome)) {}
 
 PeerConnectionFactory::PeerConnectionFactory(
     PeerConnectionFactoryDependencies dependencies)