Partly revert ad3824a90261 and add comment about reference ownership

Python/symtable.c

@@ -33,7 +33,7 @@ ste_new(struct symtable *st, identifier name, _Py_block_ty block,
     if (ste == NULL)
         goto fail;
     ste->ste_table = st;
-    ste->ste_id = k;
+    ste->ste_id = k; /* ste owns reference to k */
 
     ste->ste_name = name;
     Py_INCREF(name);
@@ -79,7 +79,6 @@ ste_new(struct symtable *st, identifier name, _Py_block_ty block,
 
     return ste;
  fail:
-    Py_XDECREF(k);
     Py_XDECREF(ste);
     return NULL;
 }