Bug 1492629 - Drop ShutdownLoaders phase, move only user to ShutdownFinal. r=mccr8

The only difference between ShutdownLoaders and ShutdownFinal was an observer service shutdown.

Differential Revision: https://phabricator.services.mozilla.com/D18389

--HG--
extra : moz-landing-system : lando

media/mtransport/nr_socket_prsock.cpp

@@ -246,7 +246,7 @@ class SingletonThreadHolder final {
 static StaticRefPtr<SingletonThreadHolder> sThread;
 
 static void ClearSingletonOnShutdown() {
-  ClearOnShutdown(&sThread, ShutdownPhase::ShutdownLoaders);
+  ClearOnShutdown(&sThread);
 }
 #endif
 

xpcom/base/ClearOnShutdown.h

@@ -48,7 +48,6 @@ enum class ShutdownPhase {
   WillShutdown,
   Shutdown,
   ShutdownThreads,
-  ShutdownLoaders,
   ShutdownFinal,
   ShutdownPhase_Length,  // never pass this value
   First = WillShutdown,  // for iteration

xpcom/build/XPCOMInit.cpp

@@ -663,7 +663,6 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
     mozilla::InitLateWriteChecks();
 
     if (observerService) {
-      mozilla::KillClearOnShutdown(ShutdownPhase::ShutdownLoaders);
       observerService->Shutdown();
     }
   }