Removed the num_instances() method from the specific_fns code as it is now part of the base class.
This method was moved to the base class in r4804 and the change was explained in a post by Edward
d'Auvergne at:
https://mail.gna.org/public/relax-devel/2008-01/msg00063.html (Message-id:
<7f080ed10801170126p7d8f5109ib838a894f4f979a8@...>)
