Do not try to import simplejson in jsonfile.py (#40983)

With the addition on ajson.py in cbb6a7f4e8, two
new classes were created: AnsibleJSONDecoder and AnsibleJSONEncoder. These
classes are used when calling json.looads() and json.dumps().

This works fine with everything except the jsonfile.py cache plugin, which would
first try to import simplejson as json, then fall back to json. When simplejson
is installed, the load() or dump methods from simplejson are called, which then
try to use the AnsibleJSONEncoder/AnsibleJSONDecoder subclass from ajson.py.
But asjon.py imports json, not simplejson, and things blow up.

lib/ansible/plugins/cache/jsonfile.py

@@ -43,11 +43,7 @@ DOCUMENTATION = '''
 '''
 
 import codecs
-
-try:
-    import simplejson as json
-except ImportError:
-    import json
+import json
 
 from ansible.parsing.ajson import AnsibleJSONEncoder, AnsibleJSONDecoder
 from ansible.plugins.cache import BaseFileCacheModule