Pretends that the swap repo never existed, by deleting it before adding
the new repo, and showing the same message that is shown when a new
repo is added. This does not change behaviour for existing non-swap
repos. They are not deleted before being added again, or else we would
lose the ability to verify the fingerprint of an existing repo is the
same as a newly added one with the same URL.
Note that this has the effect that the fingerprint/pubkey of the swap
repo is nuked when adding that repo manually.
Internationalised the string "BAD FINGERPRINT" while I was at it.
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