logilab-common #111011 [registry] inconsistent behaviour when no registration callback vs call to register_all [done]

one call load_ancestors_then_object, the other barely register all objects.

We should either find that load_ancestors_then_object is not (anymore) useless and drop it, or use it in both cases.

prioritynormal
typebug
done in0.59.0
load0.200
load left0.000
closed by#b1a0f91d9bdc [registry] use register_all when no registration callback defined. Closes #111011