Disable experimental TLS 1.3 features in default config

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index da8b6b3..5474bbd 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1720,7 +1720,7 @@
  * Uncomment this macro to enable experimental and partial
  * functionality specific to TLS 1.3.
  */
-#define MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL
+//#define MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL
 
 /**
  * \def MBEDTLS_SSL_PROTO_DTLS