Define always psa_key_id_t as defined in PSA crypto spec

Define always psa_key_id_t as defined in the PSA
Cryptography API specification independently of
whether the MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER
configuration file is set or not.

As a consequence, get rid of `psa_app_key_id_t` that is
not needed anymore.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index f0c7979..71adb93 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -232,9 +232,9 @@
     /** Number of slots that are not used for anything. */
     size_t empty_slots;
     /** Largest key id value among open keys in internal persistent storage. */
-    psa_app_key_id_t max_open_internal_key_id;
+    psa_key_id_t max_open_internal_key_id;
     /** Largest key id value among open keys in secure elements. */
-    psa_app_key_id_t max_open_external_key_id;
+    psa_key_id_t max_open_external_key_id;
 } mbedtls_psa_stats_t;
 
 /** \brief Get statistics about