Identity: remove useless error `OwnerAccountNotExist`

Identities are sufficient, so there is no need to require account existence.

added C-runtime D-hard P2-asap S-doing labels

assigned to @librelois

changed milestone to %runtime-105

changed title from Change ref counter for identities: use consumers instead of sufficient to {+Identity: remove useless error OwnerAccountNotExist+}

changed the description

removed D-hard label

removed S-doing label

added D-easy P5-sometimesoon S-ToDo labels and removed P2-asap label

changed milestone to %runtime-200

unassigned @librelois

created branch elois-63-identity-remove-useless-error-owneraccountnotexist to address this issue

mentioned in merge request !78 (merged)

closed with merge request !78 (merged)