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

webrtc/rtc_base/nullsocketserver_unittest.cc

Index: webrtc/rtc_base/nullsocketserver_unittest.cc
diff --git a/webrtc/rtc_base/nullsocketserver_unittest.cc b/webrtc/rtc_base/nullsocketserver_unittest.cc
index 5538322643a387dc73c676193ee3f7221cf34718..5908d32958a6d93d296ef7617ff73fc938343935 100644
--- a/webrtc/rtc_base/nullsocketserver_unittest.cc
+++ b/webrtc/rtc_base/nullsocketserver_unittest.cc
@@ -28,9 +28,9 @@
 };
 
 TEST_F(NullSocketServerTest, WaitAndSet) {
-  auto thread = Thread::Create();
-  EXPECT_TRUE(thread->Start());
-  thread->Post(RTC_FROM_HERE, this, 0);
+  Thread thread;
+  EXPECT_TRUE(thread.Start());
+  thread.Post(RTC_FROM_HERE, this, 0);
   // The process_io will be ignored.
   const bool process_io = true;
   EXPECT_TRUE_WAIT(ss_.Wait(SocketServer::kForever, process_io), kTimeout);