core: remove includes in .cpp, if header is already in .h

- example: if util.h includes stdint.h, remove it from util.cpp, as
  util.h is the first header included in util.cpp

src/net.cpp

@@ -15,9 +15,6 @@
 #include "db.h"
 #include "ui_interface.h"
 
-#include <inttypes.h>
-#include <stdint.h>
-
 #ifdef WIN32
 #include <string.h>
 #else