Hint Rewrite @subst_stackframe_of : subst.

Lemma remove_localdef_temp_PROP: forall (i: ident) P Q R,
EX old: val, subst i `(old) (PROPx P (LOCALx Q (SEPx R))) |--
PROPx P (LOCALx (remove_localdef_temp i Q) (SEPx R)).