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
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..