In technical sense, it is not necessary to compute the AIC to be able to compute the c-statistic. To compute the c-statistic you do need to approximate the AUC. Here's a thorough example:
The AIC and c-statistic address different aspects of model fit. Whether either needs to be reported depends on you modelling setting. For example, if you have a host of candidate models that you compare, AIC may be a useful statistic to use (although there may be better information criteria for that purpose - depends again on the specifics of your analysis situation). With this in mind, you may find this discussion relevant: