dirstate: stop using `_normallookup` in the adddrop extension

That extension is just trying to produce a "corrupted" dirstate.

Differential Revision: https://phab.mercurial-scm.org/D11433

tests/test-rebuildstate.t

@@ -17,7 +17,13 b''
   >   try:
   >     for file in pats:
   >       if opts.get('normal_lookup'):
-  >         repo.dirstate._normallookup(file)
+  >         with repo.dirstate.parentchange():
+  >             repo.dirstate.update_file(
+  >                 file,
+  >                 p1_tracked=True,
+  >                 wc_tracked=True,
+  >                 possibly_dirty=True,
+  >             )
   >       else:
   >         repo.dirstate._map.dropfile(file)
   >         repo.dirstate._dirty = True