Change the repository.PullNotes command to remove a redundant call to "ls-remote"

As noted by @linquize [here](https://github.com/google/git-appraise/commit/d9f03ea9eaa7a36b7d3116a7a48cc88e8dbb164c#commitcomment-15085557), the call to "ls-remote" in the PullNotes method is redundant; it follows a fetch of the remote refs, so they can just be listed locally instead of calling out to the remote repo again.