gh-135450: Remove assertion in _PyCode_CheckNoExternalState (gh-135466)

The assertion reflected a misunderstanding of situations where "hidden" variables might exist,
namely generator expressions and comprehensions.

Objects/codeobject.c

@@ -1999,7 +1999,6 @@ _PyCode_CheckNoExternalState(PyCodeObject *co, _PyCode_var_counts_t *counts,
                              const char **p_errmsg)
 {
     const char *errmsg = NULL;
-    assert(counts->locals.hidden.total == 0);
     if (counts->numfree > 0) {  // It's a closure.
         errmsg = "closures not supported";
     }