dirstatemap: use `set_possibly_dirty` in `clearambiguoustimes`

lets put this new method to use

Differential Revision: https://phab.mercurial-scm.org/D11121

mercurial/dirstatemap.py

@@ -261,9 +261,7 b' class dirstatemap(object):'
         for f in files:
             e = self.get(f)
             if e is not None and e.need_delay(now):
-                self._map[f] = DirstateItem(
-                    e.state, e.mode, e.size, AMBIGUOUS_TIME
-                )
+                e.set_possibly_dirty()
                 self.nonnormalset.add(f)
 
     def nonnormalentries(self):