psa: Remove buggy report of RSA public exponent for opaque keys

The report of RSA public exponent for opaque keys is not
supported. Do not attempt to compute the RSA public
exponent of an RSA opaque key associated to a driver
implementing the new driver interface when
MBEDTLS_PSA_CRYPTO_SE_C is disabled.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 7a6bb37..e571849 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1212,14 +1212,11 @@
     defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY)
         case PSA_KEY_TYPE_RSA_KEY_PAIR:
         case PSA_KEY_TYPE_RSA_PUBLIC_KEY:
-#if defined(MBEDTLS_PSA_CRYPTO_SE_C)
             /* TODO: reporting the public exponent for opaque keys
              * is not yet implemented.
              * https://github.com/ARMmbed/mbed-crypto/issues/216
              */
-            if( psa_key_slot_is_external( slot ) )
-                break;
-#endif /* MBEDTLS_PSA_CRYPTO_SE_C */
+            if( ! psa_key_lifetime_is_external( slot->attr.lifetime ) )
             {
                 mbedtls_rsa_context *rsa = NULL;