Revert of Make the default ctor of rtc::Thread, protected

webrtc/rtc_base/physicalsocketserver_unittest.cc

Index: webrtc/rtc_base/physicalsocketserver_unittest.cc
diff --git a/webrtc/rtc_base/physicalsocketserver_unittest.cc b/webrtc/rtc_base/physicalsocketserver_unittest.cc
index 34ba02789741da4b45bb5ee2b58c6b23a49afc12..ee95c2367aeb7a540e3b65bbc105fe642818e6a2 100644
--- a/webrtc/rtc_base/physicalsocketserver_unittest.cc
+++ b/webrtc/rtc_base/physicalsocketserver_unittest.cc
@@ -610,7 +610,7 @@
   // Start a new thread that raises it. It will have to be delivered to that
   // thread. Our implementation should safely handle it and dispatch
   // RecordSignal() on this thread.
-  std::unique_ptr<Thread> thread(Thread::CreateWithSocketServer());
+  std::unique_ptr<Thread> thread(new Thread());
   std::unique_ptr<RaiseSigTermRunnable> runnable(new RaiseSigTermRunnable());
   thread->Start(runnable.get());
   EXPECT_TRUE(ss_->Wait(1500, true));