py/objmodule.h: Remove obsolete mp_builtin_module_weak_links_map decl.
It was made obsolete in
#include "py/obj.h"
extern const mp_map_t mp_builtin_module_map;
-extern const mp_map_t mp_builtin_module_weak_links_map;
mp_obj_t mp_module_get(qstr module_name);
void mp_module_register(qstr qstr, mp_obj_t module);
