Simplify synchronization model in InputDevice.cpp - replaced volatile flags/mutex/condition variable with joining on thread and one atomic flag

Windows/main.cpp

@@ -674,8 +674,6 @@ int WINAPI WinMain(HINSTANCE _hInstance, HINSTANCE hPrevInstance, LPSTR szCmdLin
 
 	VFSShutdown();
 
-	InputDevice::StopPolling();
-
 	MainWindow::DestroyDebugWindows();
 	DialogManager::DestroyAll();
 	timeEndPeriod(1);