Remove some uses of atLeastPython3 (#1191)

There are a number of call sites that would behave differently depending
on Python 2 or 3. A fair amount of them are left over from Python 3.2 or
Python 2.6 were the current versions, and it was much harder to write
compatible code for both versions. Happily, that is now in the past, so
refactor some of them out.

github/GithubObject.py

@@ -231,10 +231,7 @@ class GithubObject(object):
         Converts the object to a nicely printable string.
         """
         def format_params(params):
-            if atLeastPython3:
-                items = list(params.items())
-            else:
-                items = list(params.items())
+            items = list(params.items())
             for k, v in sorted(items, key=itemgetter(0), reverse=True):
                 isText = isinstance(v, (str, six.text_type))
                 if isText and not atLeastPython3: