core: remove overzealous assertions in hwloc_obj_add_children_sets()

These were needed when this function was only internally used
a long time ago, but there's no reason the prevent other cases now
since inserting custom groups may need it.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

hwloc/topology.c

@@ -2017,9 +2017,7 @@ int
 hwloc_obj_add_children_sets(hwloc_obj_t obj)
 {
   hwloc_obj_t child;
-  assert(obj->cpuset != NULL);
   for_each_child(child, obj) {
-    assert(child->cpuset != NULL);
     hwloc_obj_add_other_obj_sets(obj, child);
   }
   /* No need to look at Misc children, they contain no PU. */