bundle2: rename duplicate handlepushkeyreply to handleobsmarkerreply

The function was only called through the parthandlermapping dict, so
it was confusing but safe in practice.

mercurial/bundle2.py

@@ -1378,7 +1378,7 b' def handleobsmarker(op, inpart):'
 
 
 @parthandler('reply:obsmarkers', ('new', 'in-reply-to'))
-def handlepushkeyreply(op, inpart):
+def handleobsmarkerreply(op, inpart):
     """retrieve the result of a pushkey request"""
     ret = int(inpart.params['new'])
     partid = int(inpart.params['in-reply-to'])