Rename available values for tls13_kex_modes

Rename `psk_pure` to `psk` and `ephemeral_pure` to `ephemeral`

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 87558f5..a339bbf 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -436,7 +436,7 @@
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
 #define USAGE_TLS13_KEY_EXCHANGE_MODES \
     "    tls13_kex_modes=%%s   default: all\n"     \
-    "                          options: psk_pure, psk_ephemeral, ephemeral_pure, ephemeral_all, psk_all, all\n"
+    "                          options: psk, psk_ephemeral, ephemeral, ephemeral_all, psk_all, all\n"
 #else
 #define USAGE_TLS13_KEY_EXCHANGE_MODES ""
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
@@ -1734,11 +1734,11 @@
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
         else if( strcmp( p, "tls13_kex_modes" ) == 0 )
         {
-            if( strcmp( q, "psk_pure" ) == 0 )
+            if( strcmp( q, "psk" ) == 0 )
                 opt.tls13_kex_modes = MBEDTLS_SSL_TLS13_KEY_EXCHANGE_MODE_PSK;
             else if( strcmp(q, "psk_ephemeral" ) == 0 )
                 opt.tls13_kex_modes = MBEDTLS_SSL_TLS13_KEY_EXCHANGE_MODE_PSK_EPHEMERAL;
-            else if( strcmp(q, "ephemeral_pure" ) == 0 )
+            else if( strcmp(q, "ephemeral" ) == 0 )
                 opt.tls13_kex_modes = MBEDTLS_SSL_TLS13_KEY_EXCHANGE_MODE_EPHEMERAL;
             else if( strcmp(q, "ephemeral_all" ) == 0 )
                 opt.tls13_kex_modes = MBEDTLS_SSL_TLS13_KEY_EXCHANGE_MODE_EPHEMERAL_ALL;