Delete TestListener and top-level thread wrapping.

Instead use rtc::AutoThread in tests that need that.

Bug: webrtc:9714
Change-Id: I1f33b1b2d321770d062504dd9ef86d66a345dd42
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/254681
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36950}
diff --git a/pc/rtp_transceiver_unittest.cc b/pc/rtp_transceiver_unittest.cc
index 680fe11..ffa5374 100644
--- a/pc/rtp_transceiver_unittest.cc
+++ b/pc/rtp_transceiver_unittest.cc
@@ -53,6 +53,7 @@
   cricket::ChannelManager* channel_manager() { return channel_manager_.get(); }
 
  private:
+  rtc::AutoThread main_thread_;
   cricket::FakeMediaEngine fake_media_engine_;
   rtc::UniqueRandomIdGenerator ssrc_generator_;
   std::unique_ptr<cricket::ChannelManager> channel_manager_;
@@ -151,6 +152,7 @@
     return sender;
   }
 
+  rtc::AutoThread main_thread_;
   rtc::scoped_refptr<MockRtpReceiverInternal> receiver_ = MockReceiver();
   rtc::scoped_refptr<MockRtpSenderInternal> sender_ = MockSender();
   rtc::scoped_refptr<RtpTransceiver> transceiver_;
@@ -222,6 +224,7 @@
     transceiver_->ClearChannel();
   }
 
+  rtc::AutoThread main_thread_;
   rtc::scoped_refptr<MockRtpReceiverInternal> receiver_ = MockReceiver();
   rtc::scoped_refptr<MockRtpSenderInternal> sender_ = MockSender();