Remove unused Py_XDECREF from _PyFrame_ClearExceptCode (GH-106158)

frame->frame_obj was set to NULL a few lines earlier.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

Python/frame.c

@@ -139,7 +139,6 @@ _PyFrame_ClearExceptCode(_PyInterpreterFrame *frame)
     for (int i = 0; i < frame->stacktop; i++) {
         Py_XDECREF(frame->localsplus[i]);
     }
-    Py_XDECREF(frame->frame_obj);
     Py_XDECREF(frame->f_locals);
     Py_DECREF(frame->f_funcobj);
 }