perf: use `setup` function in `perfdirstatewrite`

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

@@ -1192,11 +1192,13 b' def perfdirstatewrite(ui, repo, **opts):'
     ds = repo.dirstate
     b"a" in ds
 
+    def setup():
+        ds._dirty = True
+
     def d():
-        ds._dirty = True
         ds.write(repo.currenttransaction())
 
-    timer(d)
+    timer(d, setup=setup)
     fm.end()