remove references to sunrisemovement issue tracker

[skyfaller]

We misguidedly wanted to create bi-directional links between GitHub issues and code comments: sunrisemovement/devops#2. This was a huge mistake, a maintenance nightmare and harmful to portability if you forked the repo or moved to a different code forge. This might be a different story if you were using something like git-bug and all of the issues lived in the repo itself.

At any rate, all of the TODO: comments featuring links to the old issue tracker should be updated/removed, and we should avoid linking to external issue trackers from code comments. Let's stick to one-way links, from the issue tracker to the code. TODO comments are searchable from the code e.g. when offline on the train, and are fine by themselves.