refactor: don't avoid sys/types.h on when building for Windows

We've already used it unguarded in `httpserver.cpp` for years, with no
build issues.

src/test/util_tests.cpp

@@ -35,9 +35,11 @@
 #include <univalue.h>
 #include <utility>
 #include <vector>
+
+#include <sys/types.h>
+
 #ifndef WIN32
 #include <signal.h>
-#include <sys/types.h>
 #include <sys/wait.h>
 #endif