[hooks] don't insert an owned_by relation for deleted entities
If, in the same transaction, a composed entity is created and deleted,
we'll have scheduled a SyncOwnersOp which would end up creating an
owned_by relation for the deleted entity. Closes #4846883
../../doc/book usr/share/doc/cubicweb-documentation
../../doc/html usr/share/doc/cubicweb-documentation
../../debian/cubicweb-doc usr/share/doc-base/cubicweb-doc