mod_unsubscriber: Revoke roster subscriptions of unreachable hosts
Wrote a version of this long ago, but it was lost to time. Here it is
again, from scratch!
Over the years, some servers stop working for various reasons, and leave
behind broken roster subscriptions that trigger failing s2s connections.
This module allows cleaning up such cases by unsubscribing local users
from their contacts on those servers. Also works for typos and the like.
Use with care.
```lua
Component "gmail.com" "unsubscriber"
```