Red code legacy MemoryManager, StreamEngine, ResourceManager, ImageHandler, AsyncPakManager, and more (#758)

Remove from CryCommon and CrySystem:
- MemoryManager and all related classes/files
- StreamEngine, ResourceManager, ImageHandler, and AsyncPakManager
- Various other related interfaces/files/classes etc. that are all now unused

Code/CryEngine/CrySystem/LevelSystem/SpawnableLevelSystem.cpp

@@ -14,7 +14,6 @@
 #include "SpawnableLevelSystem.h"
 #include <IAudioSystem.h>
 #include "IMovieSystem.h"
-#include <IResourceManager.h>
 
 #include <LoadScreenBus.h>
 
@@ -566,8 +565,6 @@ namespace LegacyLevelSystem
 
         m_lastLevelName.clear();
 
-        GetISystem()->GetIResourceManager()->UnloadLevel();
-
         // Force Lua garbage collection (may no longer be needed now the legacy renderer has been removed).
         // Normally the GC step is triggered at the end of this method (by the ESYSTEM_EVENT_LEVEL_POST_UNLOAD event).
         EBUS_EVENT(AZ::ScriptSystemRequestBus, GarbageCollect);