remove extern definition, since it's in a header file (closes #24058)
diff --git a/Modules/readline.c b/Modules/readline.c
index f349d3b..b545bca 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1062,8 +1062,6 @@
     rl_callback_handler_remove();
 }
 
-extern PyThreadState* _PyOS_ReadlineTState;
-
 static char *
 readline_until_enter_or_signal(const char *prompt, int *signal)
 {