TLS 1.3: the key_share in a ClientHello after a HelloRetryRequest
Yes. When the client sends a new ClientHello after a HelloRetryRequest, it replaces the old KeyShare with the one the server requested in the HelloRetryRequest. This is according to my interpretation for the following text in the TLS 1.3 draft 21 here:


  the new ClientHello, the client MUST    replace the original
  "key_share" extension with one containing only a    new KeyShareEntry
  for the group indicated in the selected_group field    of the
  triggering HelloRetryRequest.


If you have any comments to confirm or correct me, please post before I accept my answer.