Reland "Drop py2 support in gerrit and git related files"

This is a reland of commit b5c7f4b46c3309d46e1796bce7fa83388af9bfd8

Original change's description:
> Drop py2 support in gerrit and git related files
>
> python3 is the only supported version of python in depot_tools.
>
> Bug: 1475402
> Change-Id: Ie4ee18d297081b3aa0206b8d7ce6461819bff0ca
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4809560
> Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
> Commit-Queue: Gavin Mak <gavinmak@google.com>

Bug: 1475402
Change-Id: I194180494071777b7b9dd91a5c8edabbbf5484c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4811218
Reviewed-by: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
diff --git a/git_number.py b/git_number.py
index f46b1ee..864f3ee 100755
--- a/git_number.py
+++ b/git_number.py
@@ -21,9 +21,6 @@
 repo that it operates on in the ref 'refs/number/commits'.
 """
 
-from __future__ import print_function
-from __future__ import division
-
 import binascii
 import collections
 import logging
@@ -60,10 +57,7 @@
   >>> pathlify('\xDE\xAD')
   'de/ad'
   """
-  if sys.version_info.major == 3:
-    return '/'.join('%02x' % b for b in hash_prefix)
-
-  return '/'.join('%02x' % ord(b) for b in hash_prefix)
+  return '/'.join('%02x' % b for b in hash_prefix)
 
 
 @git.memoize_one(threadsafe=False)
@@ -184,10 +178,7 @@
 
 
 def all_prefixes(depth=PREFIX_LEN):
-  if sys.version_info.major == 3:
-    prefixes = [bytes([i]) for i in range(255)]
-  else:
-    prefixes = [chr(i) for i in range(255)]
+  prefixes = [bytes([i]) for i in range(255)]
   for x in prefixes:
     # This isn't covered because PREFIX_LEN currently == 1
     if depth > 1:  # pragma: no cover