remove references to '2to3' in doc, travis, etc

.landscape.yml

@@ -5,17 +5,12 @@ pylint:
 
     options:
         additional-builtins:
-            # add xrange and long as valid built-ins. In Python 3, xrange is
-            # translated into range and long is translated into int via 2to3 (see
-            # "use_2to3" in setup.py). This should be removed when we drop Python
-            # 2 support (which probably won't happen any time soon).
-            - xrange
+            # add long as valid built-ins.
             - long
 
 pyflakes:
     disable:
-        # undefined variables are already covered by pylint (and exclude
-        # xrange & long)
+        # undefined variables are already covered by pylint (and exclude long)
         - F821
 
 ignore-paths: