Instead of setting `active` to `false`, we remove the device entirely
(unless its the current device).

Doing it this way means more fetching of bundles for devices that
disappear and then reappear from a user's devicelist.

However, there might be caching invalidation concerns with just reusing
a cached bundle for a device id that disappeared and then reappears.

Additionally this change simplifies the showing of a contact's device
fingerprints in the modal, since we don't have to take active/inactive
into consideration.

updates #497