mod_log_ringbuffer: Detach event handlers on logging reload (thanks Menel)
Otherwise the global event handlers accumulate, one added each time
logging is reoladed, and each invocation of the signal or event triggers
one dump of each created ringbuffer.
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"
```