core: clarify that unlink_and_free_single_object() merges children into grandparent
core: clarify that unlink_and_free_single_object() merges children into grandparent

When replacing parent with child, we need to move children to child
before calling unlink_and_free_single_object()

shekkbuilder/hwloc,shekkbuilder/hwloc,shekkbuilder/hwloc,shekkbuilder/hwloc