* we consider that it's signature will not be changed by the SUBSTITUTION_OVERRIDE, so the wrapper can be unwrapped.
     *
     * This have a few caveats when it comes to the inner classes. TODO Provide a reference to some more in-detail description of that.
     *
     * @receiver A declaration that needs to be unwrapped.
     * @return An unsubstituted declaration ([originalForSubstitutionOverride]]) if it exists and if it does not have any change