Revert "SL-18721 Viewer shutdown order changes"

This reverts commit edf0874e06.
Reverted since it causes a significant uptick in shutdown freezes.
Can't repro those freezes, will seek an alternate solution.

indra/llcommon/threadpool.cpp

@@ -21,12 +21,11 @@
 #include "llevents.h"
 #include "stringize.h"
 
-LL::ThreadPool::ThreadPool(const std::string& name, size_t threads, size_t capacity, bool auto_shutdown):
+LL::ThreadPool::ThreadPool(const std::string& name, size_t threads, size_t capacity):
     super(name),
     mQueue(name, capacity),
     mName("ThreadPool:" + name),
-    mThreadCount(threads),
-    mAutomaticShutdown(auto_shutdown)
+    mThreadCount(threads)
 {}
 
 void LL::ThreadPool::start()
@@ -40,13 +39,6 @@ void LL::ThreadPool::start()
                 run(tname);
             });
     }
-
-    // Some threads might need to run longer than LLEventPumps
-    if (!mAutomaticShutdown)
-    {
-        return;
-    }
-
     // Listen on "LLApp", and when the app is shutting down, close the queue
     // and join the workers.
     LLEventPumps::instance().obtain("LLApp").listen(

indra/llcommon/threadpool.h

@@ -31,7 +31,7 @@ namespace LL
          * Pass ThreadPool a string name. This can be used to look up the
          * relevant WorkQueue.
          */
-        ThreadPool(const std::string& name, size_t threads=1, size_t capacity=1024, bool auto_shutdown = true);
+        ThreadPool(const std::string& name, size_t threads=1, size_t capacity=1024);
         virtual ~ThreadPool();
 
         /**
@@ -66,7 +66,6 @@ namespace LL
         std::string mName;
         size_t mThreadCount;
         std::vector<std::pair<std::string, std::thread>> mThreads;
-        bool mAutomaticShutdown;
     };
 
 } // namespace LL

indra/llwindow/llwindowwin32.cpp

@@ -828,7 +828,6 @@ void LLWindowWin32::close()
 	// Is window is already closed?
 	if (!mWindowHandle)
 	{
-        mWindowThread->close();
 		return;
 	}
 
@@ -4591,7 +4590,7 @@ std::vector<std::string> LLWindowWin32::getDynamicFallbackFontList()
 #endif // LL_WINDOWS
 
 inline LLWindowWin32::LLWindowWin32Thread::LLWindowWin32Thread()
-    : ThreadPool("Window Thread", 1, MAX_QUEUE_SIZE, false)
+    : ThreadPool("Window Thread", 1, MAX_QUEUE_SIZE)
 {
     ThreadPool::start();
 }