Remove Incorrect Comment in tools/build_libtorch and remove Python2 support in the module import (#44888)

Summary:
Fixes #{44293} and removes Python2 imports from MNIST download module as Python2 is not being supported.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/44888

Reviewed By: agolynski

Differential Revision: D23785579

Pulled By: bugra

fbshipit-source-id: d9380502380876282008dd2d5feb92a446648982

tools/build_libtorch.py

@@ -8,9 +8,6 @@ import sys
 pytorch_root = dirname(dirname(abspath(__file__)))
 sys.path.append(pytorch_root)
 
-# If you want to modify flags or environmental variables that is set when
-# building torch, you should do it in tools/setup_helpers/configure.py.
-# Please don't add it here unless it's only used in LibTorch.
 from tools.build_pytorch_libs import build_caffe2
 from tools.setup_helpers.cmake import CMake
 

tools/download_mnist.py

@@ -1,18 +1,10 @@
-from __future__ import division
-from __future__ import print_function
-
 import argparse
 import gzip
 import os
+from urllib.error import URLError
+from urllib.request import urlretrieve
 import sys
 
-try:
-    from urllib.error import URLError
-    from urllib.request import urlretrieve
-except ImportError:
-    from urllib2 import URLError
-    from urllib import urlretrieve
-
 MIRRORS = [
     'http://yann.lecun.com/exdb/mnist/',
     'https://ossci-datasets.s3.amazonaws.com/mnist/',