Instead of searching and then deleting a given device-model,
just delete the given model.
The search shall be done somewhere else.
Don't free the model struct itself,
this shall be done by the invoker himself.
Don't free the device instrance list,
this shall be done by the invoker himself.
As a consequence, most DEVmodDelete() functions
collapse almost completely.
This change is of no consequence,
because DEVmodDelete() is currently nowhere used.