refactor: use <cstdio> over stdio.h

We currently use both. Consolidate on the former.

src/ipc/interfaces.cpp

@@ -12,10 +12,10 @@
 #include <tinyformat.h>
 #include <util/system.h>
 
+#include <cstdio>
 #include <functional>
 #include <memory>
 #include <stdexcept>
-#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <string>