replace MBEDTLS_KEY_EXCHANGE_SOME_NON_PFS_ENABLED with MBEDTLS_KEY_EXCHANGE_PSK_ENABLED

After the ECDH keyexchange removal the two became synonyms so the former can
be removed.

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/include/mbedtls/ssl_ciphersuites.h b/include/mbedtls/ssl_ciphersuites.h
index d3519f1..dfd3694 100644
--- a/include/mbedtls/ssl_ciphersuites.h
+++ b/include/mbedtls/ssl_ciphersuites.h
@@ -184,11 +184,6 @@
 #define MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED
 #endif
 
-/* Key exchanges that don't involve ephemeral keys */
-#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
-#define MBEDTLS_KEY_EXCHANGE_SOME_NON_PFS_ENABLED
-#endif
-
 /* Key exchanges that involve ephemeral keys */
 #if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)     || \
     defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)     || \
@@ -198,7 +193,7 @@
 #endif
 
 /* Key exchanges using a PSK */
-#if defined(MBEDTLS_KEY_EXCHANGE_SOME_NON_PFS_ENABLED)           || \
+#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)           || \
     defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
 #define MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED
 #endif