Instead of searching and then deleting a given device-instance,
just delete the given instance.
The search shall be done somewhere else.
Don't free the instance struct itself,
this shall be done by the invoker.
As a consequence most DEVdelete() functions
collapse almost completely.
This change is of no consequence,
because DEVdelete() is currently nowhere used.
MIFdelete() might be called with third arg being NULL,
searching for the instance to be deleted by name only.
Need to invoke the callback in this case too.
Allow to register a callback function in the cfunc.mod files,
which will be invoked in MIFdestroy.
Usefull to "free" memory which has been allocated locally in a cfunc.mod file.