code: public Observable<Void> purgeDeletedCertificateAsync(String vaultBaseUrl, String certificateName) {
          return purgeDeletedCertificateWithServiceResponseAsync(vaultBaseUrl, certificateName).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Permanently deletes the specified deleted certificate.
  The PurgeDeletedCertificate operation performs an irreversible deletion of the specified certificate, without possibility for recovery. The operation is not available if the recovery level does not specify 'Purgeable'. This operation requires the certificate/purge permission.
  
  @param vaultBaseUrl The vault name, for example https://myvault.vault.azure.net.
  @param certificateName The name of the certificate
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceResponse} object if successful.