Update assetManager.cpp

fix crash on exit

Engine/source/assets/assetManager.cpp

@@ -119,18 +119,6 @@ void AssetManager::onRemove()
         mAssetTagsManifest->deleteObject();
     }
 
-    purgeAssets();
-
-    for (auto itr = mDeclaredAssets.begin(); itr != mDeclaredAssets.end(); ++itr)
-    {
-       delete itr->value;
-    }
-    mDeclaredAssets.clear();
-
-    // Clear dependency graphs
-    mAssetDependsOn.clear();
-    mAssetIsDependedOn.clear();
-
     // Call parent.
     Parent::onRemove();
 }