MEDIUM: init: completely deallocate unused peers

MEDIUM: init: completely deallocate unused peers

When peers are stopped due to not being running on the appropriate
process, we want to completely release them and unregister their signals
and task in order to ensure there's no way they may be called in the
future.

Note: ideally we should have a list of all tables attached to a peers
section being disabled in order to unregister them and void their
sync_task. It doesn't appear to be *that* easy for now.