Update module_utils.six to latest (#22855)

* Update module_utils.six to latest

We've been held back on the version of six we could use on the module
side to 1.4.x because of python-2.4 compatibility.  Now that our minimum
is Python-2.6, we can update to the latest version of six in
module_utils and get rid of the second copy in lib/ansible/compat.

lib/ansible/utils/plugin_docs.py

@@ -25,7 +25,7 @@ import yaml
 
 from collections import MutableMapping, MutableSet, MutableSequence
 
-from ansible.compat.six import string_types
+from ansible.module_utils.six import string_types
 from ansible.parsing.yaml.loader import AnsibleLoader
 from ansible.plugins import fragment_loader
 
@@ -35,6 +35,7 @@ except ImportError:
     from ansible.utils.display import Display
     display = Display()
 
+
 # modules that are ok that they do not have documentation strings
 BLACKLIST = {
     'MODULE': frozenset(('async_wrapper',)),