Revert "Use libmingwex for gmtime_s"

The new version of mingw has moved all of time_s.h into time.h.

This reverts commit 1f6fdd5a306c0a08f5dcf7ef6696c2efe4839882.

Bug: http://b/26523949
Change-Id: I58f05135ac44fa053133e0cfe999054b2694b682
diff --git a/src/crypto/time_support.c b/src/crypto/time_support.c
index bf9daed..ae0f496 100644
--- a/src/crypto/time_support.c
+++ b/src/crypto/time_support.c
@@ -59,12 +59,6 @@
 #define _POSIX_C_SOURCE 201410L  /* for gmtime_r */
 #endif
 
-#if defined(__MINGW32__)
-#define MINGW_HAS_SECURE_API 1  /* supplied by libmingwex */
-#include <sec_api/time_s.h>  /* for correct definition of gmtime_s */
-#undef MINGW_HAS_SECURE_API
-#endif
-
 #include <openssl/time_support.h>
 
 #include <time.h>