Cleanup: Compositor: Ghost data of a node storage

Since 4cf7fc3b3a (where a storage handling being added) a render layer node never has persist storage data.
And even more, some code of node update do use storage field as temporal variables for a callback so no any data can live forever in this place.
No one copy/initialize/free callback of the node also does not deal with node storage.
And compositor code also don't know about node storage since use different data from a node (id and custom1 fields).

Pull Request: https://projects.blender.org/blender/blender/pulls/132717

source/blender/blenkernel/intern/node.cc

@@ -1155,7 +1155,6 @@ void node_tree_blend_read_data(BlendDataReader *reader, ID *owner_id, bNodeTree
           break;
         }
         case CMP_NODE_IMAGE:
-        case CMP_NODE_R_LAYERS:
         case CMP_NODE_VIEWER: {
           ImageUser *iuser = static_cast<ImageUser *>(node->storage);
           iuser->scene = nullptr;