infinitepush: remove unused import to tempfile

Spotted by test-check-pyflakes.t

hgext/infinitepush/store.py

@@ -8,7 +8,6 b' from __future__ import absolute_import'
 import abc
 import os
 import subprocess
-import tempfile
 
 from mercurial.pycompat import open
 from mercurial import (