Don't download pull patches

These aren't served over the API, so they can only be downloaded when
logged in. That's OK for our use case since pulls always come from a
branch in our own repo and the commits will be present in the repo
itself. The information for where to see the pull request is available
in the json.

update_repos

@@ -250,7 +250,6 @@ class PullsRepo(JsonRepo):
             self.download_file(pull.url)
             self.download_file(pull.commits_url)
             self.download_file(pull.comments_url)
-            self.download_file(pull.patch_url)
 
 class MilestonesRepo(JsonRepo):
     def __init__(self, gh_repo, config):