Correctly disable "pure_py3" doctest in plain Py2.x.

runtests.py

@@ -332,7 +332,6 @@ VER_DEP_MODULES = {
     # to be unsafe...
     (2,999): (operator.lt, lambda x: x in ['run.special_methods_T561_py3',
                                            'run.test_raisefrom',
-                                           'pure_py3',
                                            ]),
     (3,): (operator.ge, lambda x: x in ['run.non_future_division',
                                         'compile.extsetslice',

tests/run/pure_py3.py

 # mode: run
-# tag: annotation_typing
+# tag: annotation_typing, pure3.0
 
 import cython