perf: use `setup` function in `perfdirfoldmap`

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

@@ -1170,14 +1170,16 b' def perfdirfoldmap(ui, repo, **opts):'
     opts = _byteskwargs(opts)
     timer, fm = gettimer(ui, opts)
     dirstate = repo.dirstate
-    b'a' in dirstate
+    dirstate._map.dirfoldmap.get(b'a')
+
+    def setup():
+        del dirstate._map.dirfoldmap
+        del dirstate._map._dirs
 
     def d():
         dirstate._map.dirfoldmap.get(b'a')
-        del dirstate._map.dirfoldmap
-        del dirstate._map._dirs
-
-    timer(d)
+
+    timer(d, setup=setup)
     fm.end()