Remove python2 compability code (#2033)

* remove sys.version_info == 2

* remove sys.version_info < 3

* remove from __future__ imports

torchvision/datasets/stl10.py

-from __future__ import print_function
 from PIL import Image
 import os
 import os.path

torchvision/datasets/svhn.py

-from __future__ import print_function
 from .vision import VisionDataset
 from PIL import Image
 import os

torchvision/datasets/usps.py

-from __future__ import print_function
 from PIL import Image
 import os
 import numpy as np

torchvision/datasets/voc.py

 import os
-import sys
 import tarfile
 import collections
 from .vision import VisionDataset
-
-if sys.version_info[0] == 2:
-    import xml.etree.cElementTree as ET
-else:
-    import xml.etree.ElementTree as ET
-
+import xml.etree.ElementTree as ET
 from PIL import Image
 from .utils import download_url, check_integrity, verify_str_arg
 

torchvision/models/detection/_utils.py

-from __future__ import division
-
 import math
 
 import torch

torchvision/models/detection/image_list.py

 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
-from __future__ import division
-
 import torch
 from torch.jit.annotations import List, Tuple
 from torch import Tensor

torchvision/models/detection/roi_heads.py

-from __future__ import division
 import torch
 import torchvision
 

torchvision/models/detection/rpn.py

-from __future__ import division
-
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 import torch
 from torch.nn import functional as F

torchvision/models/detection/transform.py

-from __future__ import division
-
 import random
 import math
 import torch

torchvision/models/googlenet.py

-from __future__ import division
-
 import warnings
 from collections import namedtuple
 import torch

torchvision/models/inception.py

-from __future__ import division
-
 from collections import namedtuple
 import warnings
 import torch

torchvision/ops/boxes.py

-from __future__ import division
-
 import torch
 from torch.jit.annotations import Tuple
 from torch import Tensor

torchvision/ops/misc.py

-from __future__ import division
 from collections import OrderedDict
 from torch.jit.annotations import Optional, List
 from torch import Tensor

torchvision/ops/poolers.py

-from __future__ import division
-
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 import torch
 import torch.nn.functional as F

torchvision/transforms/functional.py

-from __future__ import division
 import torch
 import sys
 import math

torchvision/transforms/functional_tensor.py

-from __future__ import division
 import torch
 import torchvision.transforms.functional as F
 from torch import Tensor

torchvision/transforms/transforms.py

-from __future__ import division
 import torch
 import math
 import sys

travis-scripts/run-clang-format/run-clang-format.py

@@ -8,8 +8,6 @@ A diff output is produced and a sensible exit code is returned.
 
 """
 
-from __future__ import print_function, unicode_literals
-
 import argparse
 import codecs
 import difflib
@@ -129,11 +127,6 @@ def run_clang_format_diff(args, file):
     #   > Each translation completely replaces the format string
     #   > for the diagnostic.
     #   > -- http://clang.llvm.org/docs/InternalsManual.html#internals-diag-translation
-    #
-    # It's not pretty, due to Python 2 & 3 compatibility.
-    encoding_py3 = {}
-    if sys.version_info[0] >= 3:
-        encoding_py3['encoding'] = 'utf-8'
 
     try:
         proc = subprocess.Popen(
@@ -141,7 +134,7 @@ def run_clang_format_diff(args, file):
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             universal_newlines=True,
-            **encoding_py3)
+            encoding='utf-8')
     except OSError as exc:
         raise DiffError(
             "Command '{}' failed to start: {}".format(
@@ -150,12 +143,7 @@ def run_clang_format_diff(args, file):
         )
     proc_stdout = proc.stdout
     proc_stderr = proc.stderr
-    if sys.version_info[0] < 3:
-        # make the pipes compatible with Python 3,
-        # reading lines should output unicode
-        encoding = 'utf-8'
-        proc_stdout = codecs.getreader(encoding)(proc_stdout)
-        proc_stderr = codecs.getreader(encoding)(proc_stderr)
+
     # hopefully the stderr pipe won't get full and block the process
     outs = list(proc_stdout.readlines())
     errs = list(proc_stderr.readlines())
@@ -203,10 +191,7 @@ def colorize(diff_lines):
 def print_diff(diff_lines, use_color):
     if use_color:
         diff_lines = colorize(diff_lines)
-    if sys.version_info[0] < 3:
-        sys.stdout.writelines((l.encode('utf-8') for l in diff_lines))
-    else:
-        sys.stdout.writelines(diff_lines)
+    sys.stdout.writelines(diff_lines)
 
 
 def print_trouble(prog, message, use_colors):