perf: move some of the perftags benchmark to the setup function

Creating fresh objects and clearing the cache should not be part of the
timing.

before: ! wall 0.020851 comb 0.020000 user 0.020000 sys 0.000000 (median of 138)
after:  ! wall 0.018740 comb 0.020000 user 0.020000 sys 0.000000 (median of 141)

contrib/perf.py

@@ -537,14 +537,15 b' def perftags(ui, repo, **opts):'
     timer, fm = gettimer(ui, opts)
     svfs = getsvfs(repo)
     repocleartagscache = repocleartagscachefunc(repo)
-    def t():
+    def s():
         repo.changelog = mercurial.changelog.changelog(svfs)
         rootmanifest = mercurial.manifest.manifestrevlog(svfs)
         repo.manifestlog = mercurial.manifest.manifestlog(svfs, repo,
                                                           rootmanifest)
         repocleartagscache()
+    def t():
         return len(repo.tags())
-    timer(t)
+    timer(t, setup=s)
     fm.end()
 
 @command(b'perfancestors', formatteropts)