tests: avoid repo.lookup() for converting revnum to nodeid

Differential Revision: https://phab.mercurial-scm.org/D3050

tests/test-bundle2-remote-changegroup.t

@@ -71,8 +71,8 b' Create an extension to test bundle2 remo'
   >                part.addparam(k, str(v))
   >         elif verb == 'changegroup':
   >             _common, heads = args.split()
-  >             common.extend(repo.lookup(r) for r in repo.revs(_common))
-  >             heads = [repo.lookup(r) for r in repo.revs(heads)]
+  >             common.extend(repo[r].node() for r in repo.revs(_common))
+  >             heads = [repo[r].node() for r in repo.revs(heads)]
   >             outgoing = discovery.outgoing(repo, common, heads)
   >             cg = changegroup.makechangegroup(repo, outgoing, '01',
   >                                              'changegroup')