tls: never destroy a priavte key that is not owned/created by TLS module

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index c990b8a..9078c24 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -2622,11 +2622,8 @@
             }
 
             ssl->handshake->ecdh_psa_privkey = pk->priv_id;
-
-            if (pk_type == MBEDTLS_PK_OPAQUE) {
-                /* Key should not be destroyed in the TLS library */
-                ssl->handshake->ecdh_psa_privkey_is_external = 1;
-            }
+            /* Key should not be destroyed in the TLS library */
+            ssl->handshake->ecdh_psa_privkey_is_external = 1;
 
             status = psa_get_key_attributes(ssl->handshake->ecdh_psa_privkey,
                                             &key_attributes);