Deletes the specified IAM user. The user must not belong to any groups or have any access keys, signing certificates, or attached policies.
/// The request was rejected because it attempted to delete a resource that has attached
/// subordinate entities. The error message describes these entities.
///
/// The request was rejected because it attempted to create resources beyond the current
/// AWS account limits. The error message describes the limit exceeded.
///
/// The request was rejected because it referenced an entity that does not exist. The
/// error message describes the entity.
///
/// The request processing has failed because of an unknown error, exception or failure.
///