Fix macros in benchmark.c

#2124 may suffer from the same problem.
diff --git a/programs/test/benchmark.c b/programs/test/benchmark.c
index 74fcaa6..b005c20 100644
--- a/programs/test/benchmark.c
+++ b/programs/test/benchmark.c
@@ -31,11 +31,7 @@
 #include <stdlib.h>
 #define mbedtls_exit       exit
 #define mbedtls_printf     printf
-#define mbedtls_snprintf   snprintf
 #define mbedtls_free       free
-#define mbedtls_exit            exit
-#define MBEDTLS_EXIT_SUCCESS    EXIT_SUCCESS
-#define MBEDTLS_EXIT_FAILURE    EXIT_FAILURE
 #endif
 
 #if !defined(MBEDTLS_TIMING_C)