Ghost revision for mir-kiosk

We seem to have a ghost revision for `mir-kiosk` in the store.

With Snapcraft using the history API (4.3, rev. 5472)
```
$ snapcraft revisions mir-kiosk | head -n5
Rev. Uploaded Arch Version Channels
        2020-01-06T18:17:23Z amd64 1.6.0+dev147-snap93 edge/wayland-interface, edge/rework, stable/sighup, beta/pr48
5336 2020-10-24T14:19:18Z arm64 2.1.0+dev89-snap110 edge*
5335 2020-10-24T14:19:17Z armhf 2.1.0+dev89-snap110 edge*
5334 2020-10-24T14:08:22Z amd64 2.1.0+dev89-snap110 edge*
```

The "Channels" list for the first revision is also wrong, it should only be `edge`.

It can also be seen on https://dashboard.snapcraft.io/snaps/mir-kiosk/revisions/, see attachment.