bundle2: drop some outdated comment

bundle2: drop some outdated comment

This commend trace back to a very early bundle2 changeset c7ceae0faf69. And the
code moved past this warning over 5 years ago.

Differential Revision: https://phab.mercurial-scm.org/D9637

--- a/mercurial/bundle2.py	Fri Apr 24 16:36:04 2020 +0200
+++ b/mercurial/bundle2.py	Sat Dec 19 15:56:54 2020 +0100
@@ -1960,11 +1960,7 @@
     ),
 )
 def handlechangegroup(op, inpart):
-    """apply a changegroup part on the repo
-
-    This is a very early implementation that will massive rework before being
-    inflicted to any end-user.
-    """
+    """apply a changegroup part on the repo"""
     from . import localrepo
 
     tr = op.gettransaction()