narrow: delete a stale TODO about not sending groups the client already has

2c5835b4246b changed the changegroup generation to not send
treemanifests for directories the client had before widening. As that
commit mentions, we had already stopped before that commit to send the
changelog and filelogs for files the client already had.

Differential Revision: https://phab.mercurial-scm.org/D9898

mercurial/bundle2.py

@@ -2536,8 +2536,6 def widen_bundle(
     for r in repo.revs(b"::%ln", common):
         commonnodes.add(cl.node(r))
     if commonnodes:
-        # XXX: we should only send the filelogs (and treemanifest). user
-        # already has the changelog and manifest
         packer = changegroup.getbundler(
             cgversion,
             repo,