drop pyversion & is_python3 checking

We're committed to Python 3 at this point, so purge all the
is_python3 related dynamic checks.

Bug: https://crbug.com/gerrit/10418
Change-Id: I4c8b405d6de359b8b83223c9f4b9c8ffa18ea1a2
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/292383
Reviewed-by: Chris Mcdonald <cjmcdonald@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
diff --git a/main.py b/main.py
index cd0b862..f638a67 100755
--- a/main.py
+++ b/main.py
@@ -28,15 +28,7 @@
 import sys
 import textwrap
 import time
-
-from pyversion import is_python3
-if is_python3():
-  import urllib.request
-else:
-  import imp
-  import urllib2
-  urllib = imp.new_module('urllib')
-  urllib.request = urllib2
+import urllib.request
 
 try:
   import kerberos
@@ -68,8 +60,6 @@
 
 from subcmds import all_commands
 
-if not is_python3():
-  input = raw_input  # noqa: F821
 
 # NB: These do not need to be kept in sync with the repo launcher script.
 # These may be much newer as it allows the repo launcher to roll between