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
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a