Update atexit.cpp

Author: SchrodingerZhu

libc/src/stdlib/atexit.cpp

@@ -18,12 +18,7 @@ constinit ExitCallbackList atexit_callbacks;
 Mutex handler_list_mtx(false, false, false, false);
 [[gnu::weak]] extern void teardown_main_tls();
 
-namespace internal {
-[[gnu::weak]] extern void call_atexit_callbacks();
-}
-
 extern "C" {
-
 int __cxa_atexit(AtExitCallback *callback, void *payload, void *) {
   return add_atexit_unit(atexit_callbacks, {callback, payload});
 }