How do I use Git's interactive rebase with a local-only repository (no remote / origin)?
git rebase -i in shorthand, without specifying a destination branch, will make git assume that you are trying to rebase against a remote branch tracked by your branch. That's why the error message is mentioning stuff about remotes.
When you do specify a target, git will rebase against that commit-ish:
git rebase -i <commit-ish>
So in short - if you have 3 local commits and you now want to interactively rebase/squash/etc them:
git rebase -i HEAD~3(See Sébastien's explanation !)