Remove debugging

The "z" wasn't meant to be committed; it meant the C++17 optimization
here was never being used.

include/pybind11/pybind11.h

@@ -1400,7 +1400,7 @@ PYBIND11_NOINLINE inline void keep_alive_impl(size_t Nurse, size_t Patient, func
 
 inline std::pair<decltype(internals::registered_types_py)::iterator, bool> all_type_info_get_cache(PyTypeObject *type) {
     auto res = get_internals().registered_types_py
-#ifdef z__cpp_lib_unordered_map_try_emplace
+#ifdef __cpp_lib_unordered_map_try_emplace
         .try_emplace(type);
 #else
         .emplace(type, std::vector<detail::type_info *>());