Remove unnecessary TODO in server.py.

Refnames are checked by RefsContainer.__getitem__, which raises
KeyError if they are invalid, so we don't need to check within
apply_pack.

Change-Id: I3decc98341b7df092e7e4dfd72c1f2f3b6633992

dulwich/server.py

@@ -123,7 +123,6 @@ class GitBackend(Backend):
             status.append(('unpack', 'ok'))
 
         for oldsha, sha, ref in refs:
-            # TODO: check refname
             ref_error = None
             try:
                 if sha == ZERO_SHA: