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>

manifest_xml.py

@@ -17,15 +17,7 @@ import os
 import re
 import sys
 import xml.dom.minidom
-
-from pyversion import is_python3
-if is_python3():
-  import urllib.parse
-else:
-  import imp
-  import urlparse
-  urllib = imp.new_module('urllib')
-  urllib.parse = urlparse
+import urllib.parse
 
 import gitc_utils
 from git_config import GitConfig, IsId