hg-to-git: don't import the unused popen2 module

Importing the popen2 module in Python-2.6 results in the
"DeprecationWarning: The popen2 module is deprecated.  Use the
subprocess module." message. The module itself isn't used in fact, so
just removing it solves the problem.

Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Miklos Vajna

contrib/hg-to-git/hg-to-git.py

@@ -20,7 +20,7 @@
 """
 
 import os, os.path, sys
-import tempfile, popen2, pickle, getopt
+import tempfile, pickle, getopt
 import re
 
 # Maps hg version -> git version