localrepo: reuse exchange.bundle2requested()

It seems like localrepo.getbundle() is trying to do the same thing, so
let's just call the method. That way we get the same condition as
there (matching any "HG2" prefix, not only "HG20").

mercurial/localrepo.py

@@ -164,7 +164,7 b' class localpeer(peer.peerrepository):'
                                           **kwargs)
         cb = util.chunkbuffer(chunks)
 
-        if bundlecaps is not None and 'HG20' in bundlecaps:
+        if exchange.bundle2requested(bundlecaps):
             # When requesting a bundle2, getbundle returns a stream to make the
             # wire level function happier. We need to build a proper object
             # from it in local peer.