perf: fix the time measurement for pathcopies relative to p2

PyCharm flagged this as unused.  But it seems more likely that it was intended
to reset the time for the p2 path.

Differential Revision: https://phab.mercurial-scm.org/D7742

contrib/perf.py

@@ -2048,8 +2048,8 b' def perfhelpermergecopies(ui, repo, revs'
                 data['p1.time'] = end - begin
                 begin = util.timer()
                 p2renames = copies.pathcopies(b, p2)
+                end = util.timer()
                 data['p2.time'] = end - begin
-                end = util.timer()
                 data['p1.renamedfiles'] = len(p1renames)
                 data['p2.renamedfiles'] = len(p2renames)