Unregister a callback for tag deletion.

        Args:
            name (str): The name of the tag or tag glob.
            func (function): The callback func(node, tagname, tagval).

def offTagDel(self, name, func):
        '''
        Unregister a callback for tag deletion.

        Args:
            name (str): The name of the tag or tag glob.
            func (function): The callback func(node, tagname, tagval).

        '''
        if '*' in name:
            self.ontagdelglobs.rem(name, func)
            return

        cblist = self.ontagdels.get(name)
        if cblist is None:
            return
        try:
            cblist.remove(func)
        except ValueError:
            pass