void close() {
        applicationRepo.close();   // Closes watchers.
        sessionRepository.close(); // Closes watchers, clears memory, and deletes local files and ZK session state.
    }
Closes any watchers, thread pools that may react to changes in tenant state,
and removes any session data in filesystem and zookeeper.
Called by watchers as a reaction to deleting a tenant.
configserver/src/main/java/com/yahoo/vespa/config/server/tenant/Tenant.java