Remove unused errors like RightAlreadyAdded and RightNotExist

Some error enum variants are now unused like RightAlreadyAdded and RightNotExist. They should be removed.

see https://forum.duniter.org/t/undocumented-duniter-concepts/10168/9

changed milestone to %runtime-700

added D-easy label

changed the description

added I-ToPrioritize label

changed milestone to %runtime-701

changed milestone to %runtime-800

assigned to @bgallois

!200 (merged)

mentioned in merge request !200 (merged)

closed