New ID Copying code: fix node_tree_copy_data still potentially increasing usercount of its gpencil pointer.

_copy_data() functions of datablocks shall never handle that, it's done
by generic calling code in library.c.

source/blender/blenkernel/intern/node.c

@@ -1228,10 +1228,6 @@ void BKE_node_tree_copy_data(Main *UNUSED(bmain), bNodeTree *ntree_dst, const bN
 	/* We never handle usercount here for own data. */
 	const int flag_subdata = flag | LIB_ID_CREATE_NO_USER_REFCOUNT;
 
-	if ((flag & LIB_ID_CREATE_NO_USER_REFCOUNT) == 0) {
-		id_us_plus((ID *)ntree_dst->gpd);
-	}
-
 	/* in case a running nodetree is copied */
 	ntree_dst->execdata = NULL;