perf: do not import util.queue

This was added by af25237be091. But util.queue is not a module and is not
importable. I guess it wasn't noticed because of demandimport.

Differential Revision: https://phab.mercurial-scm.org/D1848

contrib/perf.py

@@ -27,7 +27,6 b' import struct'
 import sys
 import threading
 import time
-import util.queue
 from mercurial import (
     changegroup,
     cmdutil,