py3: use range() instead of xrange()

The latter does not exist on Python 3. This makes test-contrib-perf.t pass on
Python 3 again.

Differential Revision: https://phab.mercurial-scm.org/D6443

contrib/perf.py

@@ -408,7 +408,7 b' def _timer(fm, func, setup=None, title=N'
     count = 0
     if profiler is None:
         profiler = NOOPCTX
-    for i in xrange(prerun):
+    for i in range(prerun):
         if setup is not None:
             setup()
         func()