headers/_mingw: Undefine `MINGW_SDK_INIT`

Signed-off-by: LIU Hao <lh_mouse@126.com>

mingw-w64-headers/crt/_mingw.h.in

diff --git a/mingw-w64-headers/crt/_mingw.h.in b/mingw-w64-headers/crt/_mingw.h.in
index 3e0d544..b5e547a 100644
--- a/mingw-w64-headers/crt/_mingw.h.in
+++ b/mingw-w64-headers/crt/_mingw.h.in
@@ -668,12 +668,7 @@
 }
 #endif
 
-#endif /* _INC__MINGW_H */
-
-#ifndef MINGW_SDK_INIT
-#define MINGW_SDK_INIT
-
 #define __STDC_SECURE_LIB__ 200411L
 #define __GOT_SECURE_LIB__ __STDC_SECURE_LIB__
 
-#endif /* MINGW_SDK_INIT */
+#endif /* _INC__MINGW_H */