Remove non-PSA MAC keys in mbedtls_ssl_transform when MBEDTLS_USE_PSA_CRYPTO is defined

Also remove last usage of non-PSA MAC keys in ssl_decrypt_non_etm_cbc() SSL test.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 7445cb5..b8809fb 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -5755,9 +5755,10 @@
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     psa_destroy_key( transform->psa_mac_enc );
     psa_destroy_key( transform->psa_mac_dec );
-#endif
+#else
     mbedtls_md_free( &transform->md_ctx_enc );
     mbedtls_md_free( &transform->md_ctx_dec );
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
 #endif
 
     mbedtls_platform_zeroize( transform, sizeof( mbedtls_ssl_transform ) );