Stick to C style in header file

Author: yinyiqian1

include/utility/mpt_utility.h

@@ -1,10 +1,9 @@
 #ifndef MPT_UTILITY_H
 #define MPT_UTILITY_H
 
-#include <cstddef>
 #include <secp256k1.h>
+#include <stddef.h>
 #include <stdint.h>
-#include <vector>
 
 #ifdef __cplusplus
 extern "C" {

src/utility/mpt_utility.cpp

@@ -4,6 +4,10 @@
 #include <openssl/sha.h>
 #include <secp256k1_mpt.h>
 #include <utility/mpt_utility.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <vector>
+#include <secp256k1.h>
 
 // Platform endianness support for serialization
 #if defined(__APPLE__)