[pfsense_interface_group] Remove broken _copy_and_add_target()

- _copy_and_add_target() was broken - remove and use module base
  version.  Final fix for #74.
- Remove _copy_and_update_target() and use module base

plugins/module_utils/interface_group.py

@@ -82,26 +82,6 @@ def _validate_params(self):
     ##############################
     # XML processing
     #
-    def _copy_and_add_target(self):
-        """ create the XML target_elt """
-        self.pfsense.copy_dict_to_element(self.obj, self.target_elt)
-
-    def _copy_and_update_target(self):
-        """ update the XML target_elt """
-        before = self.pfsense.element_to_dict(self.target_elt)
-        changed = self.pfsense.copy_dict_to_element(self.obj, self.target_elt)
-        if self._remove_deleted_params():
-            changed = True
-
-        self.diff['before'] = before
-        if changed:
-            self.diff['after'] = self.pfsense.element_to_dict(self.target_elt)
-            self.result['changed'] = True
-        else:
-            self.diff['after'] = self.obj
-
-        return (before, changed)
-
     def _create_target(self):
         """ create the XML target_elt """
         self.diff['before'] = ''