fix(client): The Sync flow should not notify the browser of login after the signup confirmation poll completes.

The browser polls in the background for the status of the sign up completion itself, the client does not need to notify it of completion.

In addition, the /confirm screen should not transition to the /signup_complete screen, this causes a jerky UI.

fixes #1881
We still need to check this, but it should be moved up earlier in the flow, because that's were the browser gets notified of the unverified login.