Do not remeove macro from design doc

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/docs/proposed/config-split.md b/docs/proposed/config-split.md
index 6f3b5bd..1baab35 100644
--- a/docs/proposed/config-split.md
+++ b/docs/proposed/config-split.md
@@ -396,6 +396,7 @@
 #define MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED
 //#define MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED
 #define MBEDTLS_KEY_EXCHANGE_PSK_ENABLED
+#define MBEDTLS_KEY_EXCHANGE_RSA_ENABLED
 #define MBEDTLS_SSL_ALL_ALERT_MESSAGES
 #define MBEDTLS_SSL_ALPN
 //#define MBEDTLS_SSL_ASYNC_PRIVATE