remove python2 notes (#1279)

If I'm not mistaken python2 is no longer supported by pytorch - so removing python2-specific notes

Co-authored-by: holly1238 <77758406+holly1238@users.noreply.github.com>

Author: stas00

intermediate_source/model_parallel_tutorial.py

@@ -192,9 +192,6 @@ def train(model):
 stmt = "train(model)"
 
 setup = "model = ModelParallelResNet50()"
-# globals arg is only available in Python 3. In Python 2, use the following
-# import __builtin__
-# __builtin__.__dict__.update(locals())
 mp_run_times = timeit.repeat(
     stmt, setup, number=1, repeat=num_repeat, globals=globals())
 mp_mean, mp_std = np.mean(mp_run_times), np.std(mp_run_times)