vpx_mem.c: remove unused macro

__VPX_MEM_C__

unused since:
f58011a vpx_mem: remove vpx_memset

Change-Id: I820c972c4165275ddf21c1687748409818a7f2af
diff --git a/vpx_mem/vpx_mem.c b/vpx_mem/vpx_mem.c
index b98fe83..b261fc0 100644
--- a/vpx_mem/vpx_mem.c
+++ b/vpx_mem/vpx_mem.c
@@ -9,8 +9,6 @@
  */
 
 
-#define __VPX_MEM_C__
-
 #include "vpx_mem.h"
 #include <stdio.h>
 #include <stdlib.h>