removing deepcopy as it does not work

it cannot  handle deep crossreferenced objects
need to find alternative approach.

lib/ansible/inventory/manager.py

@@ -24,8 +24,6 @@ import os
 import re
 import itertools
 
-from copy import deepcopy
-
 from ansible import constants as C
 from ansible.errors import AnsibleError, AnsibleOptionsError, AnsibleParserError
 from ansible.inventory.data import InventoryData
@@ -260,11 +258,7 @@ class InventoryManager(object):
                 if plugin.verify_file(source):
                     try:
                         # in case plugin fails 1/2 way we dont want partial inventory
-                        inventory = deepcopy(self._inventory)
-                        plugin.parse(inventory, self._loader, source, cache=cache)
-
-                        # plugin worked! so lets use the more complete inventory
-                        self._inventory = inventory
+                        plugin.parse(self._inventory, self._loader, source, cache=cache)
                         parsed = True
                         display.vvv('Parsed %s inventory source with %s plugin' % (to_native(source), plugin_name))
                         break