perf: use `setup` function in `perfdirstate`

The command seems to pre-date the introduction of the `setup` support in timer.
We move the line that is obviously about benchmark setup in such `setup`
function.

contrib/perf.py

@@ -1112,11 +1112,13 b' def perfdirstate(ui, repo, **opts):'
     timer, fm = gettimer(ui, opts)
     b"a" in repo.dirstate
 
+    def setup():
+        repo.dirstate.invalidate()
+
     def d():
-        repo.dirstate.invalidate()
         b"a" in repo.dirstate
 
-    timer(d)
+    timer(d, setup=setup)
     fm.end()